Table of Contents

Chapter 11: Gas Exchange in Humans

Gas Exchange Surfaces

Large surface area: to allow faster diffusion.
Thin walls: to ensure diffusion is easier.
Good ventilation with air: so diffusion gradient is maintained.
Good blood supply: to maintain high concentration gradient so diffusion is faster.

The Breathing System

Structure	Description
Ribs	Bone structure that protects internal organs such as the lungs.
Intercostal Muscle	Muscles between the ribs which control their movement causing inhalation and exhalation.
Diaphragm	Sheet of connective tissue and muscle at the bottom of the thorax that helps change the volume of the thorax to allow inhalation and exhalation.
Trachea	Windpipe that connects the mouth and nose to the lungs.
Larynx	Also known as the voice box, when air passes across here we are able to make sounds.
Bronchi (Pl)	Large tubes branching off the trachea with one bronchus (singular) for each lung.
Bronchioles	Bronchi split to form smaller tubes called bronchioles in the lungs connected to alveoli.
Alveoli	Tiny air sacs where gas exchange takes place.

Cartilage in Trachea:

There is rings of cartilage around trachea.
Provides support and ensures the airways are open, so they don’t collapse when air pressure drops.

Cartilage in Trachea:

There is rings of cartilage around trachea.
Provides support and ensures the airways are open, so they don’t collapse when air pressure drops.

Volume & Pressure Changes:

Diaphragm: Thin sheet of muscle that separates the chest cavity from the abdomen and is responsible for controlling ventilation in the lungs.
Diaphragm contracts: Increased volume → decreased air pressure → air inhaled.
Diaphragm relaxes: Decreased volume → increased air pressure → air exhaled.
Internal & External intercostal muscles are antagonistic pairs.

When you inhale:

External intercostal muscles contract, pull rib up & out, which leads to increased volume, decreased pressure, and air drawn in.

When you exhale:

Internal intercostal muscles contract, pull rib down & inside, which causes decreased volume in chest cavity and increased pressure so air is forced out.
When the rate of gas exchange is increased (e.g., during physical activity), the internal intercostal muscles will pull ribs down and in to decrease volume & force air out. This is forced exhalation and it allows a greater volume of gases to be exchanged.

Breathing In:

External intercostal muscles contract
Ribcage moves up and out
Diaphragm contracts and flattens
Volume of thorax increases
Pressure inside thorax decreases
Air is drawn in

Breathing Out

External intercostal muscles relax
Ribcage moves down and in
Diaphragm relaxes and becomes dome-shaped
Volume of thorax decreases
Pressure inside thorax increases
Air is forced out

Inspired and Expired Air

Experiment:

Limewater is clear but it becomes cloudy when CO₂ is bubbled through it.
Boiling tube A will remain clear. Boiling tube B will be cloudy

Difference:

Gas	Inspired Air	Expired Air	Reason for Difference
Oxygen	21%	16%	Oxygen is removed from blood by respiring cells so blood returning to lungs has a lower oxygen concentration than the air in the alveoli, which means oxygen diffuses into the blood in the lungs.
Carbon Dioxide	0.04%	4%	Carbon dioxide is produced by respiration and diffuses into blood from respiring cells. The blood transports the carbon dioxide to the lungs where it diffuses into the alveoli as it is in a higher concentration in the blood than in the air in the alveoli.
Water Vapour	Lower	Higher	Water evaporates from the moist lining of the alveoli into the expired air as a result of the warmth of the body.
Nitrogen	78%	78%	Nitrogen gas is very stable and cannot be used by the body. For this reason its concentration does not change in inspired or expired air.

Effect of Physical Activity on Breathing

Exercise increases frequency and depth of breathing.
- To investigate this: number of breaths in a minute should be counted at rest before exercise, as well as measuring chest expansion over 5 breaths using tape measure around chest. After exercise, repeat these steps; the frequency & depth increases.
This is because cells need more oxygen to meet energy demand while exercising, and if demand isn’t met, cells respire anaerobically, producing lactic acid which must be removed because it may decrease pH in cells & denature enzymes. So, lactic acid must be oxidized, and this is known as ‘repaying the oxygen debt.’
The longer it takes to return to normal breathing, the more lactic acid is produced and the greater the oxygen debt to be repaid.

Protection for Breathing System:

Passages down to the lungs are lined with ciliated epithelial cells.
These cells have tiny hairs on the end of them that beat and push mucus up the passage towards the nose and throat where it’s removed.
Mucus is made by goblet cells.
Mucus traps particles, pathogens like bacteria or viruses, and dust, which prevents them from getting to lungs.

Chapter 12: Respiration:

Respiration: chemical process that involves the breakdown of nutrient molecules (glucose) in order to release energy stored within the bonds of these molecules.

Respiration can take place with oxygen (aerobically) or without oxygen (anaerobically). Much less energy is released for each glucose molecule broken down anaerobically compared to aerobically.

Respiration occurs in all living cells. Most of the chemical reactions in aerobic respiration take place in the mitochondria.

Humans need energy to do the following things:

Contract muscles
Synthesize protein
Cell division
Growth
Active transport
Nerve impulses
Maintain a constant internal body temperature

Gas	Aerobic	Anaerobic
Oxygen	Needed	Not needed
Glucose Breakdown	Complete	Incomplete
Products	Carbon dioxide and water	Animal cells: Lactic acid; Yeast: Carbon dioxide and ethanol
Energy Released	A lot	A little

Aerobic

Requires oxygen and is defined as the chemical reactions in cells that use oxygen to break down nutrient molecules to release energy.
Complete breakdown of glucose to release a large amount of energy for use in cell processes.
It produces carbon dioxide and water as well as releasing useful cellular energy.

Anaerobic

Doesn’t require oxygen and is defined as the chemical reactions in cells that break down nutrient molecules to release energy without oxygen.
It is incomplete breakdown of glucose and releases a small amount of energy, compared to aerobic, for use in cell processes.
Different products are produced based on type of organism.

Animals:

Muscles have high demand for energy and glucose broken down without oxygen will produce lactic acid instead.
Energy is still stored in lactic acid bonds so less energy is released.
Word equation:
- Glucose → Lactic Acid

Yeast:

Used in bread making because carbon dioxide makes bread rise and yeast in brewing where ethanol gives beer alcoholic nature and the carbon dioxide gives beer fizz.

Anaerobic Respiration Equations

Word equation:

Glucose → Alcohol + Carbon dioxide

Balanced chemical equation:

$C_{6} H_{12} O_{6} \to 2 C_{2} H_{5} OH + 2 {CO}_{2}$

The Effect of Temperature on Respiration

Time taken for methylene blue to discolor is proportional to the rate of respiration of yeast cells in suspension.
Controlled variables: dye volume, yeast suspension volume, glucose concentration, temperature & pH.
Hydrogens are released faster by the reaction, DCPIP accepts hydrogens faster until all DCPIP molecules are reduced, meaning less time is taken to become colorless.

Repaying the Oxygen Debt

During vigorous exercise, lactic acid builds up in muscle cells and lowers the pH level of the cell (making it more acidic). This could cause those enzymes in cells to be denatured, so lactic acid is excreted into the blood. Blood passes by the liver, and the lactic acid is oxidized in liver cells (lactic acid reacts with oxygen).

The waste products of lactic acid oxidation are carbon dioxide and water. This is why we breathe heavily and heart rate is high even after exercise—the lactic acid needs to be transported to the liver!

This process is called “repaying the oxygen debt.”

Chapter 13: Excretion in Humans

Humans have organs specifically for the removal of excretory products. These are the kidneys and the lungs, as well as the liver.
Excretion is the removal of waste substances of metabolic reactions, toxic materials, and substances in excess requirements.
Carbon dioxide must be excreted as it can dissolve in water to become acidic and lower the pH of the cells.
This can reduce enzyme activity in the body, which is essential to control the rate of metabolism.
Too much carbon dioxide is toxic!
Urea is also toxic in higher concentrations, so it must be excreted.

Organ	Mainly Excretes	Explanation
Lungs	Carbon dioxide	The lungs excrete carbon dioxide (a waste product of aerobic respiration) during exhalation
Kidneys	Excess water, salts, and urea	The kidneys excrete excess water, excess salts, and urea (formed in the liver from excess amino acids) by producing urine

Structure	Explanation
Kidney	Two bean-shaped organs that filter the blood
Ureter	Tube connecting the kidney to the bladder
Bladder	Organ that stores urine (excess water, salts, and urea) as it is produced by the kidney
Urethra	Tube that connects the bladder to the exterior; where urine is released

The Kidneys

The kidney is located in the back of the abdomen and has two important functions in the body:
1. Regulate water content of the blood (vital to maintain blood pressure).
2. They excrete the toxic waste products of metabolism (urea) and substances in excess.

Nephrons

Each kidney contains a million structures called nephrons, aka: kidney tubules or renal tubules.
Nephrons start in the cortex of the kidney and loop down into the medulla and back up the cortex.
Contents of the nephrons drain into the innermost part of the kidney, and the urine is collected there before it flows into the ureter to the bladder for storage.

Arterioles branch off the renal artery and lead to each nephron, where they form a knot of capillaries (glomerulus) sitting inside the cup-shaped Bowman’s capsule.

Capillaries get narrower as they get further into the glomerulus, which increases pressure on the blood (but blood here already has high pressure as it comes directly from the renal artery, which is connected to the aorta).

Smaller molecules in the blood will be forced out of the capillaries and into Bowman’s capsule, where they form the filtrate (a mix of water, salts, glucose, and urea). This process is called ultra-filtration.

Some of the substances in the filtrate are useful and will be reabsorbed back into the blood further down the nephron.

Water: reabsorbed at loop of Henle & collecting duct
Salts: loop of Henle
Glucose: proximal (first) convoluted tubule
Urea: not reabsorbed—excreted.

Reabsorption

Reabsorption of Glucose

After the glomerular filtrate enters the Bowman’s capsule, glucose is the first substance to be reabsorbed at the proximal (first) convoluted tubule.
This process takes place by active transport.
The nephron is adapted for this by having a lot of mitochondria to provide energy for active transport of glucose.
Reabsorption of glucose can’t happen anywhere else in the nephron as the proximal convoluted tubule is the only place where gates that facilitate active transport are found.
People with diabetes can’t control their blood glucose levels, and they are often very high, meaning not all glucose is filtered out of the blood and can be reabsorbed.
Since there is nowhere else for glucose to be reabsorbed, it is excreted in urine, and doctors can test urine to find out if a person is diabetic.

Reabsorption of Water and Salts

As the filtrate drips through the loop of Henle, necessary salts are reabsorbed back into the blood by diffusion.

As salts are reabsorbed back into the blood, water follows by osmosis.

Water is also reabsorbed from the collecting duct in different amounts depending on how much water is needed by the body at that time.

Role of Liver in Excretion:

Many digested food molecules absorbed in blood in the small intestine are carried to the liver for assimilation (food molecules converted to other molecules needed).
Including amino acids, used to build proteins like fibrinogen, which is a protein found in blood plasma for blood clotting.
Excess amino acids absorbed in the blood that aren’t needed to make proteins can’t be stored, so they are broken down in the process called deamination.
Enzymes in the liver split up the amino acid molecules:
- Part of the molecule containing carbon is turned into glycogen and this is stored.
- The other part with nitrogen is converted into ammonia, which is very toxic, so this is immediately converted to urea, which is less toxic.

Urea dissolves in blood and is taken to the kidney for excretion, and small amounts of urea are also excreted in sweat.

High urea levels cause:

Cell death
Reduced response to insulin, leading to diabetes
Deposits inside blood vessels

Chapter 14: Coordination and Response

Nervous System

The mammalian nervous system consists of:

Central nervous system (CNS): Consists of the brain & spinal cord.
Peripheral nervous system (PNS): Consists of nerves outside the brain and spinal cord.
The nervous system helps coordination and regulation of body functions.
Electrical impulses travel along neurons; a bundle of neurons make up a nerve.

Reflex Arc: Neural pathway that controls a reflex.

Reflex action: Means of automatically and rapidly integrating and coordinating stimuli with the responses of effectors (muscles & glands).

Synapse: Junction between two neurons.

In the synapse:
- An impulse stimulates the release of neurotransmitter molecules from vesicles into the synaptic gap.
- Neurotransmitter molecules diffuse across the gap.
- Neurotransmitter molecules bind with receptor proteins on the next neuron.
- An impulse is then stimulated in the neuron.
- Synapses ensure that impulses travel in only one direction.

Sense Organ

Sense organs are groups of receptor cells responding to specific stimuli: light, sound, touch, temperature, and chemicals.

The Eye

Cornea: Refracts light.
Iris: Controls how much light enters the pupil.
Lens: Focuses light on the retina.
Retina: Contains light receptors, some sensitive to light of different colors.
Optic nerve: Carries impulses to the brain.

The Pupil Reflex:

Reflex action carried out to protect the retina from damage.
In dim light, the pupil dilates (widens) to allow as much light in as possible.
In bright light, the pupil constricts (narrows) to prevent too much light.
The pupil reflex is controlled by a pair of antagonist muscles: radial and circular muscles.

DIAGRAM SHOWING THE EYE IN A DARK ENVIRONMENT
– PHOTORECEPTORS DETECT CHANGE IN ENVIRONMENT (DARK)
– RADIAL MUSCLES CONTRACT
– CIRCULAR MUSCLES RELAX
– PUPIL DILATES (DIAMETER OF PUPIL WIDENS)
– MORE LIGHT ENTERS THE EYE

DIAGRAM SHOWING THE EYE IN A BRIGHT ENVIRONMENT
– PHOTORECEPTORS DETECT CHANGE IN ENVIRONMENT (BRIGHT)
– RADIAL MUSCLES RELAX
– CIRCULAR MUSCLES CONTRACT
– PUPIL CONSTRICTS (DIAMETER OF PUPIL NARROWS)
– LESS LIGHT ENTERS THE EYE

ACCOMMODATION
The function of the eye in focusing on near & distant objects.
The way the lens brings fine focusing is called accommodation.
The lens is elastic and shape changes when suspensory ligaments are attached to become tight or loose.
These changes happen by contraction & relaxation of ciliary muscles.

RODS AND CONES
Rods & cones are receptor cells.
Rods are sensitive to dim light.
Cones distinguish between different colors in bright light.
There are 3 types of cone cells sensitive to different colors of light (blue, red, green).
The fovea is an area in the retina on which almost all cone cells are found.
Rod cells are found all over the retina, other than the area where the optic nerve attaches to the retina; this area is called a blind spot.

	OBJECT FAR AWAY – THE LIGHT IS REFRACTED LESS	OBJECT CLOSE BY – THE LIGHT IS REFRACTED MORE
CILIARY MUSCLES	RELAXED	CONTRACTED
SUSPENSORY LIGAMENTS	PULLED TIGHT	SLACK
LENS	THINNER	FATTER

STIMULUS	RADIAL MUSCLES	CIRCULAR MUSCLES	PUPIL SIZE	AMOUNT OF LIGHT ENTERS
DARK LIGHT	CONTRACTED	RELAXED	WIDE	MORE
BRIGHT LIGHT	RELAXED	CONTRACTED	NARROW	LESS

Homeostasis:

Maintenance of a constant internal environment.
Homeostasis keeps internal conditions under control to ensure the body can function properly.

INSULIN

Insulin is a hormone that is secreted when blood glucose is too high. This is often directly after a meal. In most cases, glucose is also excreted and lost in urine if the kidney can’t cope with glucose levels. To avoid this, insulin converts glucose to glycogen in the liver and muscles. Insulin decreases blood glucose concentration.

When We Are Hot	When We Are Cold
SWEAT IS SECRETED BY SWEAT GLANDS. THIS COOLS SKIN BY EVAPORATION. HEAT ENERGY FROM THE BODY IS LOST AS LIQUID WATER IN SWEAT BECOMES WATER VAPOUR (A STATE CHANGE).	SKELETAL MUSCLES CONTRACT RAPIDLY AND WE SHIVER. THESE INVOLUNTARY MUSCLE CONTRACTIONS NEED ENERGY FROM RESPIRATION AND SOME OF THIS IS RELEASED AS HEAT.
HAIRS LIE FLAT AGAINST THE SKIN, ALLOWING AIR TO FREELY CIRCULATE. THIS INCREASES HEAT TRANSFER TO ENVIRONMENT BY RADIATION.	ERECT HAIRS TRAP A LAYER OF AIR AROUND THE SKIN WHICH ACTS AS AN INSULATOR, PREVENTING HEAT LOSS BY RADIATION.

Negative feedback

Occurs when conditions in the body change from normal/ideal and returns back to normal/ideal.

If the level of something rises, the system reduces it.
If the level of something falls, the system increases it.

Constant cycle to ensure condition stays normal/ideal.

BLOOD GLUCOSE CONTROL

Blood glucose level is controlled by negative feedback mechanism with the production of insulin and glucagon. Both hormones are produced in the pancreas.

Insulin is produced when blood glucose rises and stimulates liver and muscle cells to convert excess glucose into glycogen to be stored.
Glucagon is produced when glucose drops and stimulates liver and muscle cells to convert stored glycogen into glucose to be released into the blood.

TYPE 1 DIABETES

Condition where insulin secreting cells in the pancreas are not able to produce insulin; this means glucose levels will be too high. It is treated by injecting insulin.

Their levels of physical activity and diet will affect the amount of insulin needed.

Skin homeostasis:

Maintaining temperature is controlled by the brain, which contains receptors sensitive to the temperature of blood. Skin also has temperature receptors; it sends impulses to the brain via sensory neurons. The brain responds by sending impulses to effectors in the skin to maintain optimum temperature (37°C) so that enzymes in the body don’t denature.

Fatty tissue acts as insulation.

Vasoconstriction: When cold, blood in capillaries slows down, and arterioles get narrower to reduce heat loss from blood.

Vasodilation: When hot, blood in capillaries increases, capillaries get wider, and this cools the body as blood flows faster, so more heat is lost by radiation.

Trophic responses

Involuntary movement of organisms in response to environmental stimuli.

Gravitropism: response in which plants grow away from/towards gravity.
Phototropism: response in which parts of plants grow towards/away from the direction of the light source.
Positive tropism: towards stimulus.
Negative tropism: away from stimulus.

Plant shoots have a positive phototropic and negative gravitropic response.

Plants respond to stimuli by producing a growth hormone called Auxin. It controls the direction of growth of roots or stems. Plants control their growth chemically.

Auxin is made in the shoot tip.
Auxin diffuses through the plant from the shoot tip.
Auxin is unequally distributed in response to light and gravity.
Auxin stimulates cell elongation.

Chapter 15: Drugs

Drug

Any substance taken into the body that modifies or affects the chemical reactions in the body.
Some drugs are medicinal and are used to treat symptoms or causes of a disease.
The liver is the primary site for drug metabolism.

Antibiotics

Antibiotics are used for the treatment of bacterial infections.
Chemical substances made by certain fungi or bacteria that affect the working of bacterial cells either by disrupting the structure or function or by preventing them from reproducing.
Antibiotics target bacterial (prokaryotes) cells specifically. They don’t harm animal cells.

Antibiotic Use & Resistance

Antibiotics are widely overused. Commonly prescribed antibiotics are less effective due to:
- Overusage when not needed
- Failing to complete the prescribed course
- Use of antibiotics in farming

Antibiotic resistance is increasing, and these bacteria are called superbugs. Example: MRSA.
To prevent antibiotic resistance:

Only use antibiotics when necessary.
Ensure that the entire prescribed course is completed.

Bacteria	Virus
Some bacteria is resistant to antibiotics, which reduces their efficiency.	Antibiotics can kill bacteria but not viruses.
	Viruses don’t have cell walls that can be attacked by antibiotics.

Chapter 16: Reproduction

Asexual Reproduction

Reproduction that doesn’t involve sex cells or fertilization.
Only one parent is required, offspring are genetically identical to the parent and to each other (clones).
Asexual reproduction is a process resulting in the production of genetically identical offspring from one parent.

Advantages:

Population can rapidly increase with the right conditions.
Can exploit a suitable environment quickly.
More time and energy efficient.
Reproduction is completed faster compared to sexual reproduction.

Disadvantages:

Limited genetic variation.
Population vulnerable to changes in the environment.
Disease is more likely to affect the whole population due to the lack of genetic variation.

Sexual Reproduction

Sexual reproduction is the process involving the fusion of nuclei of two gametes to form a zygote and the production of offspring that are genetically different from each other.
Fertilisation is the fusion of the nuclei of two gametes.
The nuclei of gametes is haploid, but the zygote is diploid.

Advantages:

Increased genetic variation.
Species adapt to new environments, giving survival advantages.
Disease is less likely to affect the population due to genetic variation.

Disadvantages:

Takes time and energy to find mates.
Difficult for isolated members to reproduce.

Sexual Reproduction in Humans

Male Reproductive System:

Structure	Function
Prostate Gland	Produces fluid called semen that provides sperm cells with nutrients.
Sperm Duct	Sperm passes through the sperm duct to be mixed with fluids produced by the glands before being passed into the urethra for ejaculation.
Urethra	Tube running down the center of the penis that can carry out urine or semen. A ring of muscle in the urethra prevents the urine and semen from mixing.
Testis	Contained in a bag of skin (scrotum) and produces sperm (male gamete) and testosterone (hormone).
Scrotum	Sac supporting the testes outside the body to ensure sperm are kept at a temperature slightly lower than body temperature.
Penis	Passes urine out of the body from the bladder and allows semen to pass into the vagina of a woman during sexual intercourse.

Female Reproductive System:

Structure	Function
Oviduct	Connects the ovary to the uterus and is lined with ciliated cells to push the released ovum down it. Fertilization occurs here.
Ovary	Contains ova (female gametes) which will mature and develop when hormones are released.
Uterus	Muscular bag with a soft lining where the fertilized egg (zygote) will be implanted to develop into a fetus.
Cervix	Ring of muscle at the lower end of the uterus to keep the developing fetus in place during pregnancy.
Vagina	Muscular tube that leads to the inside of the woman’s body, where the male’s penis will enter during sexual intercourse and sperm are deposited.

Adaptive features of Sperm:

Flagellum to let it swim to the egg.
Mitochondria to provide energy to flagellum to swim.
Enzymes in acrosome to digest into the jelly coat of the egg.

Adaptive features in Egg cells:

Energy stores for dividing zygote after fertilization.
Jelly coat that changes during fertilization forms an impenetrable barrier so no more sperms enter the egg.

	SPERM	EGG
SIZE	Very small (45 μm)	Large (0.15 mm)
STRUCTURE	Head region and flagellum, many structural adaptations	Round cell with few structural adaptations, covered in a jelly coating
MOTILITY	Capable of locomotion	Not capable of locomotion
NUMBERS	Produced every day in huge numbers (around 100 million per day)	Thousands of immature eggs in each ovary, but only one released each month

Pregnancy

In early development, the zygote forms an embryo, which is a ball of cells that implants into the lining of the uterus. When the fetus (after placenta forms, embryo is called fetus) is developing:

Umbilical Cord: Joins the fetus to the placenta for nutrient and waste exchange.
Placenta: Provides nutrients, removes waste, produces hormones for baby growth.
Amniotic Sac: Protects the fetus from injury by acting as a cushion.
Amniotic Fluid: Protects the fetus from injury and temperature changes.

Placenta & Umbilical Cord

The fetus grows and develops by gaining glucose, amino acids, fats, water, and oxygen, all from the mother’s blood.
Blood runs opposite and never mixes from placenta, fetus blood connects to and from placenta via the umbilical cord.
The mother’s blood collects waste (CO₂, urea, etc.) and removes it from the fetus.
Movement of all these molecules occurs by diffusion due to concentration gradient. The placenta has a large surface area and is thin, acting as a barrier to toxins.
Some pathogens and toxins (e.g., rubella, nicotine) can pass through the placenta and affect the fetus.

Sexual Reproduction in Plants

Structure	Description
Sepal	Protects unopened flower
Petals	Brightly colored in insect-pollinated flowers to attract insects
Anther	Produces and releases the male sex cell (pollen grain)
Stigma	Top of the female part of the flower which collects pollen grains
Ovary	Produces the female sex cell (ovum)
Ovule	Contains the female sex cells (found inside the ovary)

Feature	Insect-Pollinated

Petals	Large and brightly colored to attract insects
Scent and Nectar	Present – entices insects to visit the flower and push past stamen to get to nectar
Number of Pollen Grains	Moderate – insects transfer pollen grains efficiently with a high chance of successful pollination
Pollen Grains	Larger, sticky and/or spiky to attach to insects and be carried away
Anthers	Inside flower, stiff and firmly attached to brush against insects
Stigma	Inside flower, sticky so pollen grains stick to it when an insect brushes past

Feature	Wind-Pollinated

Petals	Small and dull, often green or brown in color
Scent and Nectar	Absent – no need to waste energy producing these as no need to attract insects
Number of Pollen Grains	Large amounts – most pollen grains are not transferred to another flower so the more produced, the better the chance of some successful pollination occurring
Pollen Grains	Smooth, small and light so they are easily blown by the wind
Anthers	Outside flower, swinging loose on long filaments to release pollen grains easily
Stigma	Outside flower, feathery to catch drifting pollen grains

Pollination is the transfer of pollen grains from an anther to a stigma.

Self-pollination: Transfer of pollen from anther to stigma on the same plant/flower.
Cross-pollination: Transfer of pollen from anther to stigma on a different plant.

Fertilization in plants occurs when pollen nucleus fuses with an ovum nucleus in the ovule. Pollen lands on stigma, pollen slips down a tube (style) grown to ovary, ovary contains 1 or more ovules which contain ovum.

Once nuclei of ovum and pollen join, a zygote is formed. The zygote will become a seed.

Germination:

Growth of seed at the start.

Factors needed:

Water: Seed swells up, and enzymes start working.
Oxygen: Energy for respiration is released.
Warmth: Reactions happen faster, helping enzymes.

Sexual Hormones in Humans

Secondary Sexual Characteristics are changes that occur during puberty; these changes are controlled by hormones:

Oestrogen in women
Testosterone in men.

Menstrual Cycle:

28 days long period controlled by hormones from the ovary and pituitary gland.
Ovulation occurs halfway through; failure to fertilize the released egg causes menstruation.
It is caused by the breakdown of the thickened lining of the uterus and it lasts around 5-7 days.

Hormone changes:

Oestrogen rises from day 1-14, the uterus wall thickens as the egg matures.
Progesterone starts to rise after ovulation; if the egg is fertilized, the increasing levels cause the uterus lining to thicken further. The fall in progesterone causes the lining to break down.
FSH (Follicle-Stimulating Hormone): Released by the pituitary gland and causes the egg to start maturing, stimulates ovaries to release oestrogen.
LH (Luteinising Hormone): If oestrogen reaches a peak, LH is released by the pituitary gland to make ovulation occur and stimulate the ovary to produce progesterone.

FEMALE	EFFECTS OF OESTROGEN
	– Breasts develop
	– Body hair grows
	– Menstrual cycle begins
	– Hips get wider

MALE	EFFECTS OF TESTOSTERONE
	– Growth of penis and testes
	– Growth of facial and body hair
	– Muscles develop
	– Voice breaks
	– Testes start to produce sperm

Sexually Transmitted Infections

Sexually transmitted infection (STI) is an infection transmitted through sexual contact/intercourse.

Human Immunodeficiency Virus (HIV) is a pathogen that causes STI. HIV infection may lead to AIDS.

HIV can be transmitted via the exchange of body fluids of people with HIV, such as blood, breast milk, semen, and vaginal secretions.

During pregnancy, if the mother has HIV, so will the child.

Spread of STI & HIV is controlled by:

Limiting the number of sexual partners.
Not having unprotected sex (use condoms).
Getting tested occasionally.
Raising awareness via education programs.

Chapter 17: Inheritance

Chromosomes, genes & proteins

Inheritance: Transmission of genetic info from generation to generation.
Chromosomes are located in the nucleus of cells, thread-like DNA structures carrying genetic info in the form of genes.
Gene is a short length of DNA found in chromosomes that codes for specific protein.
Alleles are different versions of a particular gene; alleles give all organisms their characteristics.

DNA Base Sequence to Amino Acid Sequence

The DNA code (a series of bases) is converted into proteins (a series of amino acids).
The process of protein synthesis has two main stages:
1. Transcription: Rewriting base code DNA into RNA.
2. Translation: Using RNA to build amino acid into sequence.
Therefore, the sequence of bases in DNA determines the sequence of amino acids that make a specific protein.
Different sequences give different shapes and functions to protein molecules.

The Inheritance of Sex

Sex is determined by a chromosome pair. Females have the XX sex chromosome, and males have the XY sex chromosome. As only the father can pass the Y chromosome, he is responsible for determining the sex of the baby. This is because, out of all sperm ejaculated, half is X chromosome, and the other half is Y. Inheritance can be shown in a genetic diagram called Punnett Squares, where X and Y take place of alleles in the diagram.

Transcription & Translation

Proteins are made by ribosomes with sequences of amino acids controlled by the sequence of bases in DNA. DNA can’t travel out of the nucleus because it is too big.

Protein Synthesis

Gene coding for protein remains in the nucleus.
Messenger RNA (mRNA) is a copy of a gene.
mRNA molecules are made in the nucleus and move to the cytoplasm of the cell.
mRNA passes through ribosomes.
Ribosome reads mRNA and assembles amino acids into protein molecules.
The specific sequence of amino acids is determined by the sequence of bases in mRNA.

Control of Gene Expression

Expression of a gene means whether the gene is transcribed and translated in a cell or not. Most genes aren’t expressed because that might waste energy.

Haploid & Diploid

All humans have 23 different chromosomes in each cell. In body cells (excluding sex cells), we have two copies of each chromosome, making the total 46 chromosomes.

Haploid nucleus: Nucleus with a single set of chromosomes.
Diploid nucleus: Nucleus with 2 sets of chromosomes. A diploid cell has a pair of each type of chromosome. Human diploid cells have 23 pairs (46 individually).

Mitosis

Mitosis is nuclear division giving rise to genetically identical cells.
Mitosis is required in growth, repair of damaged tissues, and replacement of cells and asexual reproduction.
Exact replication of chromosomes occurs before mitosis and during mitosis copies of chromosomes separate, maintaining the chromosome number in each daughter cell.
Daughter cell: Either of the two cells formed when a cell undergoes cell division (mitosis).
Stem cells: Unspecialized cells that divide by mitosis to produce daughter cells that can become specialized for specific functions.

Meiosis

Meiosis is involved in the production of gametes.
Meiosis is the reduction division in which the chromosome number is halved from diploid to haploid, resulting in genetically different cells.

Monohybrid Inheritance

Genotype: Genetic makeup of an organism/combination of alleles that control each characteristic.
Phenotype: Observable features of an organism (Seen by looking or found, e.g., eye color, blood group).
Homozygous: Having 2 identical alleles of a gene, e.g., (bb or BB). Two identical homozygous individuals that breed together will be pure-breeding, e.g., two dogs of the same breed.
Heterozygous: Having 2 different alleles of a particular gene (Bb or Aa). Breeding among heterozygous individuals will not be pure breeding.
Dominant Allele: Allele that is expressed if it is present in the genotype.
Recessive Allele: Allele that is expressed when dominant alleles aren’t present.
Codominance: Situation in which both alleles in heterozygous organisms contribute to the phenotype.
Sex-linked Characteristic: Feature in which gene responsible is located on sex chromosome, which leads to characteristic being more common in one sex compared to the other. For example, red-green color blindness is a sex-linked characteristic that’s more common in males.

Monohybrid Inheritance: Inheritance of characteristics controlled by a single gene, e.g., petal color of a plant.

Codominance and Sex Linked Characteristics

Genotype	Phenotype
$I^{A} I^{A} or I^{A} I^{O}$	A
$I^{B} I^{B} or I^{B} I^{O}$	B
$I^{A} I^{B}$	AB
$I^{O} I^{O}$	O

Genetic Diagrams: Pedigree Diagrams

Pedigree diagrams trace the pattern of inheritance of specific characteristics through generations. They can be used to predict the probability of inheriting a genetic disorder.

Males are usually represented by squares, and females by circles.
Individuals affected by a characteristic are shown in red.
Individuals unaffected are shown in blue.
Horizontal lines show connections and produced children.

Punnett Squares

Punnett Squares show possible combinations for alleles. From this, ratios can be worked out.

Dominant allele is represented with a capital letter and recessive with a lowercase letter. The dominant allele is always written first.
- Example:
  - TT, tt – homozygous
  - Tt – heterozygous

To construct a Punnett Square:

Determine parental genotype.
Select letters with a clear difference between uppercase and lowercase (e.g., Bb).
Split alleles and place them in the Punnett Square.
It gives the probability of different outcomes from monohybrid crosses.

Monohybrid Cross

A Monohybrid Cross is the hybrid of two homozygous genotypes, which results in the opposite phenotype of a certain genetic trait.

Example: Crossing TT (tall) and tt (short) gives Tt (tall).

Test Cross

A Test Cross is used to determine the genotype of an organism showing a dominant phenotype.

Procedure:
1. Cross the unknown individual with an individual showing the recessive phenotype.
2. If the offspring show the recessive phenotype, the unknown individual’s genotype must be homozygous recessive.
Interpretation:
- If all offspring display the dominant phenotype, the unknown parent is likely homozygous dominant.
- If the offspring show a mix of dominant and recessive phenotypes, the unknown parent is heterozygous.

Calculating Phenotypic Ratios:

Chapter 18: Variation and Selection

Variation

Variation: The difference between individuals of the same species.

Phenotypic Variation: Differences in features between individuals of the same species.

There are two types of phenotypic variation:

Continuous Variation: Small degrees of difference, usually measured on a scale (e.g., height, mass, finger length).
Discontinuous Variation: Distinct differences with no intermediates (e.g., blood group, gender, having an ability).

How is phenotypic variation caused? Genetic or Environmental.

Genetic:
- Controlled by genes (e.g., blood group, eye color, gender, ability to roll tongue).
- Discontinuous variation is caused by genetic variation only.
- Genes determine inherited characteristics, while the environment influences development.
Environmental:
- Caused by the environment in which an organism lives (e.g., weight, scarring, accents).
- Environmental factors like climate, diet, lifestyle, and accidents affect these variations.

Adaptive Features

Adaptive Feature: Inherited functional features of an organism that increase its fitness. Fitness is the probability of an organism surviving and reproducing in its environment.

Hydrophyte

Hydrophyte: Plants adapted to live underwater.

Common adaptations include:
- Large air spaces in leaves to keep them close to the surface of the water.
- Small roots to extract nutrients from the surrounding water through their tissues.
- Stomata are usually open and found on the upper epidermis to exchange gases easier.

Xerophyte

Xerophyte: Plants adapted to live in extreme, dry conditions.

Adaptations include:
- Thick, waxy cuticle—barrier to evaporation, shiny to reflect sunlight.
- Sunken stomata—traps moisture, reduces evaporation.
- Small leaves—reduce surface area for evaporation.
- Extensive shallow roots—large water absorption fast.
- Thickened leaves/stem—more water stored.
- Leaf rolled—reduces transpiration, causes covered in hairs that prevent air movement.

Mutation

Random genetic changes to the base sequence of DNA are called mutations.
- They usually have no effect on phenotype; rarely, mutations lead to the development of new alleles and have a small effect on organisms.
- Occasionally, a new allele gives a survival advantage over other individuals in the species.
- Mutations can also lead to harmful changes that have significant effects, such as sickle cell anemia.
Mutations happen spontaneously and continuously, but the frequency is increased by exposure to:
- Gamma rays, X-rays, and ultraviolet rays (ionizing radiation damaging bonds and causing changes in base sequences).
- Certain types of chemicals (e.g., tar in tobacco).
Increased mutation rates can cause cells to become cancerous.

Source of Genetic Variations

Mutations: New alleles form through changes to DNA.
Meiosis: New allele combinations form through segregation (separation of alleles).
Random Mating: Partnerships for sexual reproduction.
Random Fertilization: Sperm and egg combinations during sexual reproduction.

Natural Selection	Artificial Selection
Occurs naturally.	Only occurs when humans intervene.
Results in the development of populations with features that are better adapted to their environment and survival.	Results in the development of populations with features that are useful to humans and not necessarily to the survival of the individual.
Usually takes a long time to occur.	Takes less time as only individuals with the desired features are allowed to reproduce.

Natural Selection

Individuals with the best adaptive features are most likely to survive and reproduce, and this is natural selection. Individuals show a range of variation due to genes, and they produce more offspring than the environment can support. This causes competition or “struggle for survival.”

Survival of the Fittest: Individuals that are most suited to the environment have more chances for survival and reproduction. Their characteristics are passed to offspring at a higher rate, leading to better-adapted variations over time. This is Charles Darwin’s theory of natural selection, known as “Survival of the Fittest.”

Chance Mutations Lead to Less Snails Having White Shells: White-shelled snails survive longer because they are better camouflaged and less likely to be seen by predators. Since they survive longer, they reproduce more, and over generations, the process is repeated until the majority of snails have white shells.

Environmental Change: If the environment doesn’t change, selection doesn’t change, favoring individuals with the same characteristics as their parents. If the environment changes, chance mutations produce new alleles, and selection favors individuals with different characteristics. These individuals survive longer, reproduce more, and pass different sets of alleles to their offspring. Change in characteristics brings evolution. Evolution is a change in adaptive features of a population over time as a result of natural selection.

Antibiotic Resistant Bacteria:

Chapter 19: Organisms & Their Environment

Transfer of Energy

The Sun is the principal source of energy input for biological systems.
Energy flows through living organisms, including light energy from the Sun and chemical energy in organisms.
Energy is eventually transferred back to the environment, e.g., heat.

Pyramids of Number & Biomass

Pyramid of Numbers: Shows how many organisms are at each trophic level; the width of each box represents the number of organisms.

Pyramids of numbers don’t always have to be pyramid-shaped. The size of the organism is important.
Rules: When drawing pyramids of numbers, you can’t change the trophic level of organisms; it must be the same order as the food chain.
Size Factor: The larger an organism is, the less of them are available (usual cases).

Pyramid of Biomass: Shows how much mass the creatures at each level would have without including water (only dry mass).

It should always be pyramid-shaped. This is because the mass of organisms has to decrease as you move up the food chain.
Importance: It’s impossible for 1 kg of frogs to feed 50 kg of insects.
Pyramids of biomass give a better idea of the quantity of plant/animal at each level, representing interdependence.

Food Chains and Food Webs

Source of Energy: The source of all energy in a food chain is light energy from the Sun.
Arrows: The arrows in food chains show the transfer of energy from one trophic level to the next by ingestion.
Energy Transfer: Energy is transferred from one organism to the next by ingesting it. A food chain shows the transfer of energy from one organism to the next, starting with the producer.

Term	Definition
Producers	Organisms that produce their own organic nutrients usually using energy from sunlight. Plants are producers as they carry out photosynthesis to make glucose.
Herbivore	An animal that gets its energy by eating plants.
Carnivore	An animal that gets its energy by eating other animals.
Primary Consumers	Herbivores – they feed on producers (plants).
Secondary Consumers	Predators that feed on primary consumers.
Tertiary Consumers	Predators that feed on secondary consumers.
Decomposers	Bacteria and fungi that get their energy from feeding off dead and decaying organisms and undigested waste (such as faeces) by secreting enzymes to break them down.

A food web is a network of interconnected food chains.

Connections: Shows connections between organisms as animals rarely exist on just one food source.
Energy Transfer: Shows the transfer of energy in an ecosystem.
Human Impact: Changes in the population of animals and plants happen due to overharvesting food species or the introduction of foreign species to habitats.

Nutrient Cycles

The Carbon Cycle

There is a finite amount of carbon, and it needs to be recycled in order to allow new organisms to be made and grow.
Carbon is taken out of the atmosphere as carbon dioxide by plants for photosynthesis. It is passed onto other organisms by feeding.
Carbon is returned to the atmosphere in the form of carbon dioxide as a result of respiration in animals.
If plants or animals die in conditions where decomposing microorganisms are not present, the carbon in their bodies won’t convert, and it turns into fossil fuels.
When fossil fuels are burned (combustion), carbon combines with oxygen and carbon dioxide is released.
Increased fossil fuel usage leads to increased carbon dioxide, mass deforestation leads to the loss of producers to take in carbon dioxide, and trees burnt down release more carbon dioxide into the air.

The Nitrogen Cycle

Nitrogen is an element required to make proteins; neither plants nor animals can absorb it from the air. There are two ways in which nitrogen is taken out of the air and converted into something easy to absorb:
- Nitrogen-fixing bacteria: Take N₂ and change it into nitrates in the soil.
- Lightning can “fix” N₂ gas—splits bonds and turns them into nitrous oxides that dissolve in rainwater.
Plants absorb nitrates in the soil, use nitrogen in them to make proteins; animals eat plants and get nitrogen from proteins in plants; waste (faeces) returns nitrogen back into the soil as ammonium compounds.
Plants can’t absorb ammonium compounds, so a second type of soil bacteria, nitrifying bacteria, converts ammonium compounds to nitrites and then to nitrates.
Another type of bacteria is unhelpful: anaerobic bacteria called denitrifying bacteria found in poorly oxygenated soils.
These bacteria take nitrates in soil and convert them back to N₂ gas; farmers reduce these bacteria by ploughing and turning over the soil.

Pyramids of Energy

For energy to be transferred, it has to be consumed.

Not all energy made by producers is passed onto consumers as the plant uses energy for other living functions.
Only energy made into new cells remains within the organism to be passed on.
Even then, some energy isn’t consumed. Energy is stored in parts that aren’t eaten (e.g., roots) so it isn’t passed.
Energy is lost/used by:
- Making waste products
- Movement
- Heat (body temperature)
- Undigested faeces

This is why food chains are rarely longer than 5 organisms.

Energy Transfer in a Human Food Chain

Humans are omnivores (eat both plants and animals), and this gives us a choice of what we eat.
This choice of food impacts what we grow and how we use ecosystems.

Example:

Wheat → Cows → Humans
Wheat → Human

Logically, more energy is available if we eat wheat directly, as energy isn’t lost from cows. It is more efficient within crop food chains for humans to be herbivores rather than carnivores.

Note: In reality, we feed animals on plants we can’t eat or ones that are too widely distributed to collect, e.g., grass and algae.

Populations

Population: A group of organisms from the same species living in the same area at the same time.

Community: All populations of different species in an ecosystem.

Ecosystem: A unit containing a community of organisms and their environment, interacting together.

Living organisms compete for food, water, and living space. Population growth is controlled by:

Food supply
Predation
Disease

Population Growth Curve

This is a Sigmoid growth curve. It has 4 distinct phases:

Lag Phase: Organisms are adapting to the environment. In this phase, there are fewer organisms, so less reproduction happens.
Log Phase (Exponential Phase): Food supply is abundant, birth rates are rapid, death rates are low, and growth is exponential.
Stationary Phase: Population levels out due to factors in the environment becoming limited, and birth and death rates become equal.
Death Phase: Population decreases due to a shortage of food supply, accumulation of metabolic wastes, and toxic levels built up by the population.

Organisms in the natural environment are unlikely to show a Sigmoid growth curve as they are affected by many other factors, such as:

Changing light/temperature
Predators
Disease
Immigration and emigration

Chapter 20: Human influences on ecosystems

Ensuring Food Supply

Making food production intensive means producing it efficiently with finite resources. Modern technology has significantly increased food supply through the following methods:

Agricultural machinery: Improved efficiency and the ability to farm more land.
Chemical fertilizers: Improve crop yield.
Insecticides and herbicides: Kill pests and weeds, leading to less crop damage.
Selective breeding: Reliably produces high yields.

Monocultures:

Monoculture refers to growing only one type of crop in a given area, which doesn’t happen naturally. In the wild, there are many different species of plants that support a diverse range of animals, leading to high biodiversity. Monocultures have low biodiversity and can increase pest populations, leading farmers to use more pesticides and insecticides. However, this can result in:

Harmless insects being killed
Persistent chemicals entering the food chain
Pests becoming resistant to chemicals

The Importance of Biodiversity

REASON	EXPLANATION

CLEARING LAND FOR FARMING AND HOUSING

– Crops, livestock, and homes all take up a large amount of space.
– As there is an increasing population and demand for food, the amount of land available for these things must be increased by clearing habitats such as forests (deforestation).

EXTRACTION OF NATURAL RESOURCES

– Natural resources such as wood, stone, and metals must be gathered to make different products.
– Therefore many trees are cut down, destroying forest habitats. In addition, some resource extraction takes up a large amount of space.
– For example: mining, which means that the land must be cleared first.

MARINE POLLUTION

– Human activities lead to the pollution of marine habitats.
– In many places, oil spills and other waste pollute the oceans, killing sea life.
– In addition, eutrophication can occur when fertilizers from intensively farmed fields enter waterways.
– This causes a huge decrease in biodiversity in these areas as most aquatic species living in these waterways die from lack of oxygen.

Biodiversity refers to the number of different species that live in an area. Human activities can reduce biodiversity, but high biodiversity is essential for stable ecosystems. Habitat destruction is a major cause of biodiversity loss.

Reasons for Habitat Destruction:

Increased area for housing, crop, and livestock production
Extraction of natural resources
Freshwater and marine pollution (littering and waste disposal)

EFFECT	CONSEQUENCE
EXTINCTION / LOSS OF BIODIVERSITY	– Forest habitats, especially tropical rainforests, have a huge range of biodiversity, and as habitat is destroyed, it causes the loss of large numbers of plant and animal species. – Many of these species are only found in these areas and therefore will become extinct.
SOIL EROSION	– Tree roots help to stabilize the soil, preventing it from being eroded by rain. – Trees will usually take up nutrients and minerals from the soil through their roots. – Without trees, nutrients and minerals will remain unused in the soil, so they will be washed away into rivers and lakes by rain (leaching). – This loss of soil nutrients is permanent and makes it very difficult for forest trees to regrow, even if the land is not cultivated with crop plants or grass for cattle.
FLOODING	– Without trees, the topsoil will be loose and unstable, so it will be easily washed away by rain, increasing the risk of flash flooding and landslides.
INCREASED CARBON DIOXIDE IN ATMOSPHERE	– Trees carry out photosynthesis during which they take in carbon dioxide and release oxygen. – The removal of significant numbers of trees means less carbon dioxide is being removed from the atmosphere (and less oxygen released). – When areas of land in forests are cleared for land use, the trees are often burned as opposed to being cut down. This releases carbon dioxide (it is an example of combustion), further increasing carbon dioxide levels in the atmosphere and contributing to global warming.

DEFORESTATION

Clearing of trees (on a large scale).
If trees are replanted, it can be a sustainable practice.
Trees are cleared for different land use purposes.
Deforestation is a severe example of habitat destruction as it leads to:
- Extinction of species
- Loss of soil
- Flooding
- Carbon dioxide increase in the atmosphere.

Water pollution

POLLUTANT	SOURCE / CAUSE	EFFECT
UNTREATED SEWAGE	Lack of sewage treatment plants in inhabited areas (due to poor infrastructure / lack of money) meaning sewage runs / is pumped into streams or rivers.	Provides a good source of food for bacteria, which increase rapidly, depleting the oxygen dissolved in the water (as they respire aerobically) and causing death of aquatic organisms such as fish – known as eutrophication.
CHEMICAL WASTE	Chemicals such as heavy metals like mercury can be released from factories into rivers and oceans or leach into land surrounding the factories.	Many heavy metals and other chemicals are persistent – they do not break down and so can build up in food chains (known as bioaccumulation), poisoning the top carnivores.
DISCARDED RUBBISH	Much rubbish consists of plastic that is either discarded or buried in landfills.	Much rubbish, such as that made from plastic, is non-biodegradable and remains in the environment for hundreds of years. Animals also eat the plastic as it breaks into smaller pieces (especially in the ocean) and it can get into food chains this way.
FERTILISERS	Runoff from agricultural land if applied in too high a concentration.	Causes algal blooms which then die and provide a good source of food for decomposing bacteria which increase rapidly, depleting the oxygen dissolved in the water (as they respire aerobically) and causing death of aquatic organisms such as fish – known as eutrophication.
INSECTICIDES & HERBICIDES	Sprayed on crops to prevent damage by insects and growth of weeds.	Bioaccumulation, loss of biodiversity, damage to beneficial insects, can build up in soil to toxic concentrations and harm other organisms.
NUCLEAR FALLOUT	Radioactive particles that get into the environment from accidental leakage from nuclear power plants or explosion of a nuclear bomb.	Some radioactive particles have long half-lives and can remain in the environment for many years. They can cause increased risks of cancer and smaller particles can be carried by winds hundreds of miles from the original site of exposure.
METHANE	Cattle farming, rice fields, landfills.	Methane is a greenhouse gas which contributes to the enhanced greenhouse effect that is causing climate change.
CARBON DIOXIDE	Produced when fossil fuels are burnt, also released when forests are burnt to clear land for human use.	Carbon dioxide is a greenhouse gas which contributes to the enhanced greenhouse effect that is causing climate change.

Eutrophication

Fertilizer runoff from farms enters water and causes increased growth of algae.
‘Algal bloom’ blocks sunlight, so water at the bottom dies, and algae competition for nutrients will be too high.
When all algae dies, decomposed bacteria increases and use up dissolved oxygen, and aquatic organisms (e.g., fish) die due to not being able to breathe.

Sustainability

A sustainable resource is something that is produced as rapidly as it is used, so it doesn’t run out.
Fossil fuels (coal, oil, gas) are non-renewable. They need to be conserved by reducing the amount used and finding sustainable replacements.
Fossil fuels are an energy source and raw material for other products, e.g., oil used in plastic making.
Plastic, paper, glass, and metal can be recycled.
Resources like fish and forests can be harvested sustainably so they won’t run out.

Sustainable development:

Sustainable development provides for the needs of an increasing population without environmental harm.
For this to be done, conflicting demands must be balanced:
- Local people utilize large companies by selling resources.
- Balancing human needs with plant and animal needs.
- Balancing what the current population and future generations will need.
For sustainable development, people need to cooperate at local, national, and international levels in planning and managing resources.

Forest management:

Forests needed for paper and wood for timber must be replanted when the mature trees are cut. Wood is made sustainable by the introduction of several schemes and monitoring of logging companies.
Education helps keep companies aware of issues.

Fish stocks:

Fish stocks are managed by controlling the number and size of fish caught and controlling the time of year that certain fish are caught.
Restocking (letting fish breed and offspring grow).
Educating fishermen and consumers about fish that aren’t produced sustainably to avoid them.

Other pollution

CAUSES	SOURCES	EFFECTS	POSSIBLE SOLUTIONS
SULPHUR DIOXIDE, OXIDES OF NITROGEN	– Burning of fossil fuels – Combustion of petrol in car engines	1. Damage to leaves, killing plants; 2. Acidification of lakes, killing animals; 3. Increased risk of asthma attacks and bronchitis in humans; 4. Corrosion of stonework on buildings; 5. Release of aluminium from the soil into lakes that are toxic to fish.	1. Changing the power stations from coal and oil to renewable energy sources. 2. Using ‘scrubbers’ in power station chimneys to reduce sulphur dioxide. 3. Using catalytic converters in car exhausts to convert oxides of nitrogen to harmless nitrogen.

Plastic Pollution

Plastic has a negative impact due to its non-degradeability.
In marine habitats:
- Animals eat or get stuck in the plastic.
- When plastic degrades, it releases toxins.
- When degraded into very small pieces, it enters the food chain.
On land:
- Plastic is buried in landfills; as it breaks down, toxins are released into the soil and land, which is good for crops or grazing animals.

Air Pollution

Combustion of fossil fuels that contain sulfur creates sulfur dioxide, and in the atmosphere, it combines with oxygen to become sulfur trioxide, which dissolves in water droplets in clouds and becomes acid rain.

Methane & Carbon Dioxide

Both gases insulate Earth, and higher levels of these gases lead to global warming and climate change. Human activity has increased the amount of these gases by:
- Burning fossil fuels (releases carbon dioxide).
- Keeping livestock (generates methane gas).
- Global warming melts permafrost that releases more methane.

Endangered Species

Species at risk of extinction are endangered, meaning their population is critically low, which may be due to:
- Hunting
- Climate change
- Pollution
- Habitat loss
- Introduction of non-native species
Endangered species can be helped by conservation measures such as:
- Education programs
- Captive breeding programs
- Monitoring and legal protection
- Seed banks for plants
If there isn’t enough genetic variation, remaining organisms are all similar and won’t have adaptations to survive in case of environmental changes.
Moral, cultural, and scientific reasons for conservation:
- Reducing extinction
- Protecting vulnerable ecosystems
- Protecting our future food supply by maintaining nutrient cycles and sources of medicinal drugs and fuels.

Reasons for Conservation

Maintaining/increasing biodiversity
Reducing extinction
Protecting vulnerable ecosystems
Maintaining ecosystem functions: nutrient cycling, resource provision of food, drugs, fuel, and genes.

Conservation techniques to maintain biodiversity:

Artificial insemination (AI):
- Allows a large number of offspring to be produced without the need for conventional sexual intercourse.
- Used in captive breeding programs.
In vitro fertilization (IVF):
- Used in captive breeding programs.
- Allows gametes with known alleles to be used in ensuring the next generation remains biodiverse.

Risk to a Species:

If population declines, species will have reduced genetic variation.
This leaves species more likely to be harmed by environmental changes.
Species are less resilient and at greater risk of extinction.

Chapter 21: Biotechnology & Genetic Modification

Bacteria in Biotechnology

Microorganisms can be used by humans to produce foods and other useful substances—the most common microorganisms used in biotechnology is bacteria.
They are useful because they are capable of producing complex molecules and they can reproduce rapidly, meaning chemicals they can produce will also rapidly increase.
They also have fewer ethical concerns over manipulation and growth when using them to grow large numbers in laboratories.
Bacteria also possess plasmids, which are small, circular loops of DNA, which can be an ideal way of transferring DNA from one cell to another during genetic modification.

Genetic Modification

Genetic modification is changing the genetic material of an organism by removing, changing, or inserting individual genes from another organism.
The organism receiving genetic material is said to be ‘genetically modified’ or is described as a transgenic organism.
The DNA of the organism with DNA from another organism combined is known as ‘Recombinant DNA.’

Process of Genetic Modification Using Bacterial Production of a Human Protein

Isolation of DNA making the human gene using restriction enzymes, forming sticky ends.
Cutting bacterial plasmid DNA with the same restrictive enzymes forming complementary sticky ends.
Inserting human DNA into bacterial plasmid DNA using DNA ligase to form a recombinant plasmid.
Insert recombinant plasmid into bacteria.
Multiplication of bacteria containing recombinant plasmids.
Expression in bacteria of the human gene to make the human protein.

Examples of Genetic Modification

Insertion of human gene into bacteria to make human proteins.
Insertion of genes into crops to make them resistant to insect pests.
Insertion of genes into crops to resist herbicides.
Insertion of genes into crops to improve nutritional quality.

Advantages and disadvantages of genetically modifying crops like maize, soya, and rice:

ADVANTAGES	DISADVANTAGES
Reduced use of chemicals such as herbicides and pesticides – better for the environment. Cheaper/less time-consuming for farmers.	Increased costs of seeds – companies that make GM seeds charge more for them to cover the cost of developing them. This can mean smaller, poorer farmers cannot compete with larger farms.
Increased yields from the crops as they are not competing with weeds for resources or suffering from pest damage.	Increased dependency on certain chemicals, such as the herbicides that crops are resistant to – often made by the same companies that produce the seed and more expensive to buy.
	Risk of inserted genes being transferred to wild plants by pollination, which could reduce the usefulness of the GM crop (e.g., if weeds also gain the gene that makes them resistant to herbicide).
	Reduced biodiversity as there are fewer plant species when herbicides have been used – this can impact insects and insect-eating birds.
	Some research has shown that plants that have had genes inserted into them do not grow as well as non-GM plants.

Everyday Usage of Biotechnology

Yeast is a single-celled fungus that uses sugar as its food source. When it respires, ethanol and carbon dioxide are produced (energy is also released). Ethanol is used as a biofuel (fuel made from living organisms and not fossil fuels like oil or coal). Plant material is used as a substrate for producing ethanol—chopped, mixed with yeast to respire and produce ethanol (concentrated ethanol solution). Waste parts of the crop are used, but crops are grown specifically to produce ethanol. In some places, this causes concerns as too much land is used.

Yeast respires anaerobically if it has access to sugar even if oxygen is available. This is used in bread-making, where yeast is mixed with flour and water and respires to produce carbon dioxide. This CO₂ is caught in the bread and causes it to rise.

Chopping fruits before squeezing helps release a lot more juice, but this doesn’t break open all cells, so juice is lost. By adding pectinase to chopped fruit, it breaks chemical pectin in plant cell walls. Once the pectin is broken down, cell walls break easily, and more juice can be squeezed.

Adding pectinase also produces clearer juice as larger polysaccharides like pectin make juice cloudy, so when broken, juice is clearer.

Many stains on clothes are organic molecules (oil from skin), but detergents that have soap only can remove some stains when in hot water, but it takes a lot of effort and time. By adding a lightweight enzyme, biological washing powders have enzymes like digestive ones, so they can quickly break large, insoluble molecules into smaller ones so they dissolve in washing powder and are more effective at lower temperatures, meaning less energy (and money) has to be used. These washing powders can be used on delicate fabrics that aren’t suitable for higher temperatures.

Lactose is sugar in milk. Humans are born with the ability to produce lactase, but many people can lose this ability as they grow older, and they become lactose intolerant. The enzyme lactase is then added to milk before consuming lactose. Milk is lactose-free by adding lactase to it to break down lactose.

Penicillin was the first antibiotic discovered by Alexander Fleming in 1928 when he noticed bacteria was being killed by some naturally occurring Penicillium mold. Penicillium mold produced chemicals to prevent infection from certain bacteria. Ever since its discovery, penicillin has been produced on a large scale in industrial fermenters, where microorganisms in large amounts can be used to produce antibiotics.

Genetically modified bacteria and the advantage of fermenters is that the conditions can be carefully controlled to produce the exact right type of bacteria or fungus.

Condition	Why and how it is controlled
Nutrients	Nutrients are needed for use in respiration to release energy for growth and reproduction of the microorganisms.
Optimum temperature	Temperature is monitored using probes and maintained using a water jacket. This ensures an optimum environment for enzymes to increase enzyme activity and prevent denaturation.
Optimum pH	pH is monitored using a probe to check it is at the optimum value for the microorganism being grown. The pH can be adjusted using acids and alkalis.
Oxygenation	Oxygen is required for aerobic respiration to take place.
Waste	The contents are filtered to remove waste created by the microorganisms.

Mycoprotein

Fusarium is grown in large quantities and in aerobic conditions with glucose syrup provided as a food source to allow respiration.
The fungal biomass is harvested and purified to produce mycoprotein.
Mycoprotein is a protein-rich food suitable for vegetarians.

Insulin

The gene for human insulin has been inserted into bacteria, which then produces human insulin that can be collected and purified for medical use to treat diabetic people.

Chapter 11: Gas Exchange in Humans

Gas Exchange Surfaces

The Breathing System

Cartilage in Trachea:

Cartilage in Trachea:

Volume & Pressure Changes:

Breathing In:

Breathing Out

Inspired and Expired Air

Experiment:

Difference:

Effect of Physical Activity on Breathing

Protection for Breathing System:

Chapter 12: Respiration:

Aerobic

Word equation:

Balanced chemical equation:

Repaying the Oxygen Debt

Chapter 13: Excretion in Humans

Chapter 14: Coordination and Response

Synapse: Junction between two neurons.

Sense Organ

Homeostasis:

Trophic responses

Chapter 15: Drugs

Drug

Antibiotics

Antibiotic Use & Resistance

Chapter 16: Reproduction

Asexual Reproduction

Sexual Reproduction

Sexual Reproduction in Humans

Male Reproductive System:

Female Reproductive System:

Pregnancy

Sexual Reproduction in Plants

Sexual Hormones in Humans

Chapter 17: Inheritance

Transcription & Translation

Codominance and Sex Linked Characteristics

Genetic Diagrams: Pedigree Diagrams

Punnett Squares

Monohybrid Cross

Test Cross

Calculating Phenotypic Ratios:

Chapter 18: Variation and Selection

Variation

Adaptive Features

Hydrophyte

Xerophyte

Mutation

Source of Genetic Variations

Natural Selection

Antibiotic Resistant Bacteria:

Chapter 19: Organisms & Their Environment

Transfer of Energy

Pyramids of Number & Biomass

Food Chains and Food Webs

Nutrient Cycles

The Carbon Cycle

The Nitrogen Cycle

Pyramids of Energy

Energy Transfer in a Human Food Chain

Populations

Population Growth Curve

Chapter 20: Human influences on ecosystems

Ensuring Food Supply

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Monocultures:

The Importance of Biodiversity

Reasons for Habitat Destruction:

Water pollution

Other pollution

Chapter 21: Biotechnology & Genetic Modification

Everyday Usage of Biotechnology

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