Biology paper 1 AQA GCSE

Microscopes

Light microscope: cheap, can see cell outline

Electron microscope: finer details including organelles due to greater resolving power and higher definition

micrometer

'μ'

Equal to 1x10^-6 meters

Or 1000th of a mm

Animal and plant cell organelles

Cell membrane- semi permeable: controls what enters and exits

Nucleus- DNA

Mitochondria- respiration

Ribosomes- protein synthesis

Cytoplasm - where chemical reactions happens

Only plant cell organelles

Chloroplasts- hold chlorophyll for photosynthesis

Cell wall- cellulose for rigidity

Permanent vacuole- holds sap

Prokaryote cells

DNA is loose in cytoplasm

Mitosis

1. Genetic material duplicates

2. Nuclear membrane dissolves

3. Two sets of chromosomes line up at centre of cell

4. Sets pulled to either side of cell

5. New nuclei forms

6. Other organelles duplicate and cell divides

7. 2 identical diploid cells

Specialisation

Stem cells can specialise to perform specific functions

Stem cells

Found in embryos and meristems

(also in bone marrow, but those can only specialise into blood cells- so can be used for diabetes treatment)

Can be used in GM crops or to preserve a species

Embryo Clones

Make clone of an embryo of a person, extract stem cells

Done so they won't be rejected

Diffusion

Movement of particles down the concentration gradient

Passive- no energy

Increase: difference in concentrations, surface area, temperature

Osmosis

Diffusion of water through a semi-permeable membrane to balance concentration of solutions

Must be water to move because larger particles can't fit through

Active transport

Movement of particles through a membrane via carrier proteins

Requires energy, can go against concentration gradient

Osmosis practical

Weigh identical vegetable pieces and place in varying concentrations of sugar solutions

After set time, remove from solution, dry to remove excess liquid, reweigh

Calculate change in mass

Plot graph

At 0% change in mass, the concentrations were equal

Organisation of human systems

Cell, tissue, organ, organ system

DS: Mouth

Teeth break down food mechanically

Saliva contains amylase

DS: Stomach

Churns food together with hydrochloric acid and enzymes

DS: Liver

Produces bile- stored in gall bladder before going to small intestine

Bile emulsifies lipids into small droplets, increasing surface area for better digestion

DS: Pancreas

Secretes amylase which breaks down starch into glucose in the small intestine

DS: Small intestine

Nutrients absorbed by villi

However starch is too large

DS: Large intestine

Water absorbed

Enzymes

Special proteins that act as biological catalysts, breaking down molecules into shorter ones (polymers to monomers)

Specific- only breaking down molecules that fit its active site (lock and key model)

Enzyme Denaturation

Temperature increases enzyme activity until denature (when the active site changes shape)

Same is true for pH

Optimum= the condition for maximum activity

Digestive enzymes

Carbohydrases break down carbohydrates into simple sugars

Proteases break down proteins into amino acids

Lipases break down lipids into glycerol and fatty acids

Enzyme practical

Mix amylase and starch, start timer

Every ten seconds, add drop to iodine-filled spotting tray

Record time taken for no starch to be detected, shown by no colour change in the iodine

Repeat at different temperatures or pHs

Food tests

Starch- iodine turns black

Sugar- Benedict's solution goes from blue to brick red

Protein- Biuret's reagent goes from blue to purple

Lipids: cold ethanol goes cloudy or Sudan III splits into 2 layers, with the top being brick red

Lung components

Trachea: wind pipe

Bronchi: split off pipes

Bronchioles: branches

Alveoli: air sacs

Alveoli

Large surface area for gas exchange

Many capillaries for increased diffusion

Oxygen diffuses into blood stream and CO2 and water also diffuse out

Circulatory system type

Double circulatory system: blood enters heart twice every time it is pumped around the body

Right side of heart

deoxygenated blood

Vena carva: into right atrium from body

Valve separates atrium and ventricle to prevent backflow

Pulmonary artery: out of right ventricle into lungs

Left side of heart

oxygenated blood

Aorta: out of left ventricle into body

Valve separates atrium from ventricle

Pulmonary vein: into left atrium from lungs

Heart adaptations

Thicker wall on left ventricle for higher pressure to pump blood

Cells in wall of right atrium create electrical impulses to cause contraction- can be replaced with an artificial pacemaker if not working

Artery

carries blood away from the heart

Thick walls, thin lumen to withstand pressure

Capillary

1 cell thick for fast diffusion

Vein

Carries blood back to heart

Thin walls, thick lumen, valves to prevent back-flow (can be replaced artificially)

Blood carries

Red blood cells, white blood cells, platelets

Everything except oxygen is dissolved into plasma

CVD

cardiovascular disease

Fat builds up in arteries- restricting blood flow

Stents- hold vessel open

Statins- reduce fatty deposits

Pros of stents

Blood flow to heart muscle cells is increased

Remains in place for a long time

Effect is immediate

Cons of stents

Risk of infection

Risk of blood clots

Pros of statins

Not invasive

Low cost (compared to stents)

Slows down build up of fatty materials in arteries

Cons of statins

Side effects- muscle pain

Drug must be taken long term

Effects take time to happen

CHD

coronary heart disease

Artery supplying heart with blood gets blocked

Non communicable diseases

Internal cause e.g:

Diabetes: obesity and poor diet

Heart disease: smoking, diet, lack of exercise

Liver disease: alcohol

Lung disease: smoking

Cancer

Disease caused by mutation in cells causing uncontrollable multiplication

Carcinogens increase risk

Benign= don't spread

Malignant= spreads and grows

Plant components

Leaf- photosynthesis, gas exchange

Flower- reproductive organ

Meristem- stem cells

Phloem- carries sugar and nutrients through translocation (bidirectional)

Xylem- carries water and mineral ions through transpiration (unidirectional)

Roots- water enters via osmosis, mineral ions via active transport

Leaf structure (top to bottom)

1. waxy cuticle

2. upper epidermis

3. palisade mesophyll layer with chloroplasts

4. spongy mesophyll layer

5. vascular bundle through spongy mesophyll layer

6. lower epidermis

7. guard cells and stoma

Waxy cuticle

At top, waterproof to stop water loss

Upper epidermis-

transparent, lets light through

Palisade mesophyll

Most photosynthesis happens here

spongy mesophyll

Gaps to facilitate gas exchange (large s.a)

Vascular bundle

Xylem and phloem- embedded in spongy mesophyll

Lower epidermis

Bottom of leaf

Stomata

Holes in lower epidermis to allow gas and water in/out

Guard cells

change size to control entrance to stomata

Pathogens

Pathogens: micro-organisms that cause disease (bacteria, viruses, fungi, protists)

Viruses

Reproduce by injecting genes into cells and produce more copies

Bacteria

Release toxins into your body that damage cells

Fungi

Damage cells

Protists

Single-celled organisms- carried by a vector

Plant diseases

Rose black spot- causes leaves to fall off

Tobacco mosaic virus- discolours leaf, limiting photosynthesis

Defences

Human: skin=barrier, Mucus=trap

Plants: Cell wall= barrier, poison/thorns= deterrent

Immune defence

Lymphocytes: type of WBC- produces anti-toxins to neutralise toxins

Produces antibodies to bind to the antigen of a pathogen (only if it fits) causing clumping and preventing spread

Phagocytes: other type of WBC- ingest pathogens

T-Cells store antibodies ready for next time (immunity)

Vaccines

The insertion of a dead or inert version of a virus- body gains immunity without becoming ill

Anti-Biotic flaws

Only kill bacteria

Hard to make them target only bad bacteria

Whole course must be taken or situation can get worse (resistant bacteria)

Natural drugs

Aspirin- painkiller from willow

Penicillin- antibiotic from mould

Drug Trials

Expensive

Trialed for efficacy, toxicity, dosage

Tested on:

1. Cell tissue

2. Animals

3. Humans

Blind trials: test group+control group don't know which group they're in

Double-blind trial: doctors don't know who has the placebo either- removes bias

photosynthesis

H2O+CO2—> C6H12O6+O2

Water + carbon dioxide —> glucose + oxygen

Glucose used for:

Respiration, making starch or fat energy stores, cellulose, amino acids for proteins

Rate of photosynthesis increase by:

Increase temp

Increase light intensity

Increase CO2 concentration

Photosynthesis practical

Fill inverted measuring cylinder with water and sodium hydrogen carbonate (for CO2)

Place pondweed in, measure distance from light source

Allow acclimatisation, then count bubbles in set time

Repeat at different distances

Respiration

Aerobic: Gluscose + oxygen —> water + carbon dioxide

Anaerobic (animal): glucose —> lactic acid

Anaerobic (plant): glucose —> ethanol + carbon dioxide (fermentation)

Oxygen Debt

After anaerobic respiration, lactic acid must be removed

Liver converts back into glucose using oxygen (must breathe to pay back oxygen debt)

Exercise

Increases heart and breathing rates to allow increase in blood flow to supply muscles with more oxygen and glucose

Metabolism

The sum of all chemical reactions in a cell or organism

Why might oil be placed on top of a solution in an experiment

To keep oxygen from surroundings out

What does reduced photosynthesis cause

Reduced glucose production

Why do heart attack survivors get out of breath easily

Heart muscle cannot pump as effectively

So less blood is pumped out of heart

So less oxygen reaches cells for respiration

So breathing rate has to increase to supply more oxygen

How do plants intake water

Osmosis through root hair cells

How are phloem's companion cells adapted

Pores in end walls so dissolved sugars can move from cell to cell

Few organelles to maximise space for movement of sugars

Why is it important for sugar to travel both up and down phloem

Sugars are made in the leaves

All cells need sugars for respiration

Need to be transported for storage

Uses of sugar in the body

Respiration

To form glycogen

To make amino acids

As an energy source

To make fat

Why would bacterial diseases go up in the summer

Warmer weather allows bacteria to reproduce faster

How can oxygen production show the rate of photosynthesis

Measure the volume of oxygen produced in a given amount of time

Why might using the optimal conditions for photosynthesis not give a farmer maximum profit

There is a cost for heating, increasing carbon dioxide, and lighting a greenhouse

Therefore the additional costs might exceed the profit

Why does a plant produce negative oxygen in a situation of 0lux

No light means no photosynthesis

So no oxygen produced

But respiration still happens so oxygen is used

Therefore the overall oxygen production is negative

Why are healthy patients used in early clinical trials?

There is too great a risk for an ill person

The side effects may be harder to identify with an ill person

Why must clinical trial results be peer approved?

To prevent false claims

To ensure validity

Binary fission

Prokaryotes like bacteria reproduce by binary fission — DNA replicates, cytoplasm splits, two identical cells form.

Magnification formula

Image size ÷ actual size = magnification (units must match)

Villi adaptations

Large surface area, good blood supply, thin wall — for fast nutrient absorption

Bile is alkaline

Neutralises stomach acid to provide optimum pH for enzymes in the small intestine

How vaccines lead to immunity

Dead/inactive pathogens stimulate white blood cells to produce antibodies — memory cells remain for faster response on re-exposure

Monoclonal antibodies

Produced from identical cloned white blood cells — used in pregnancy tests, targeting drugs to cancer cells

Limiting factors graph shape

Photosynthesis rate increases then plateaus when a different factor becomes limiting

What is the formula to calculate magnification?

Magnification = Image Size ÷ Actual Size

Why do you add iodine to a microscope slide?

To stain cells and make structures like the nucleus visible.

What is cell differentiation?

The process by which a cell becomes specialised for its function.

How do plant cells differ in differentiation from animal cells?

Plants can differentiate throughout their life; animals mostly in early development.

What are stem cells?

Undifferentiated cells that can divide to form any cell type.

Why are some people against using embryonic stem cells?

Ethical/religious reasons – destroying a potential life.

Name three parts of a bacterial cell not found in animal cells.

Plasmid DNA, cell wall (not cellulose), flagella.