GCSE Biology Syllabus

What happens to an enzyme at temperatures above its optimum or at extreme pH?

The active site changes shape (the enzyme denatures) so the substrate can no longer fit, and the enzyme stops working. Rate of reaction rapidly falls to zero.

How are villi adapted for the absorption of digested food?

Villi provide a large surface area, have a thin wall (one cell thick) for a short diffusion distance, a rich blood supply to maintain a concentration gradient, and contain a lacteal for absorbing lipid products.

Name the three types of blood vessel and one key feature of each.

Arteries — carry blood away from the heart at high pressure, thick muscular/elastic walls, narrow lumen. Veins — carry blood to the heart at low pressure, thinner walls, wide lumen, contain valves to prevent backflow. Capillaries — one-cell-thick walls for exchange of substances with tissues.

Describe the pathway of blood through the heart (double circulation).

Deoxygenated blood enters the right atrium (from vena cava), goes to the right ventricle, and is pumped to the lungs via the pulmonary artery. Oxygenated blood returns via the pulmonary vein to the left atrium, goes to the left ventricle, and is pumped to the body via the aorta.

Why is the left ventricle wall thicker than the right ventricle wall?

The left ventricle pumps oxygenated blood all around the body at high pressure, so it needs a thicker, more muscular wall. The right ventricle only pumps blood a short distance to the lungs at lower pressure.

What are the four components of blood and one function of each?

Red blood cells — carry oxygen (contain haemoglobin). White blood cells — defend against pathogens. Platelets — help blood clot. Plasma — a liquid that transports blood cells, nutrients, CO2, urea, hormones and heat.

How are red blood cells adapted to carry oxygen?

They have a biconcave disc shape for a large surface area, contain haemoglobin which binds oxygen (forming oxyhaemoglobin), and have no nucleus so there is more room for haemoglobin.

How is the rate of blood flow calculated?

$$\text{rate of blood flow} = \frac{\text{volume of blood}}{\text{time}}$$ For example, in $\text{cm}^{3}/\text{min}$.

What are coronary arteries and what happens in coronary heart disease?

Coronary arteries supply oxygenated blood to the heart muscle. In coronary heart disease, fatty material builds up in these arteries, narrowing them and reducing blood flow, so the heart muscle receives less oxygen — which can cause a heart attack.

Name the three main plant tissues involved in transport and support, and their functions.

Xylem — transports water and dissolved mineral ions from roots to leaves (transpiration stream); made of dead hollow cells strengthened with lignin. Phloem — transports dissolved sugars (translocation) from leaves to the rest of the plant, both up and down. Epidermal/mesophyll tissues carry out other roles.

Compare xylem and phloem.

Xylem: dead cells, hollow tubes with no end walls, strengthened by lignin, one-way flow upwards, carries water and minerals. Phloem: living cells with sieve plates and companion cells, two-way flow (translocation), carries dissolved sugars (sucrose).

What is transpiration and name factors that increase its rate.

Transpiration is the loss of water vapour from a plant's leaves (mainly through stomata) by evaporation and diffusion. Rate increases with higher temperature, increased air movement (wind), lower humidity, and higher light intensity (stomata open).

What is the role of guard cells and stomata?

Stomata are pores (mainly on the lower epidermis of leaves) that allow gas exchange ($\ce{CO2}$ in, $\ce{O2}$ out) and let water vapour escape. Guard cells surround each stoma and open or close it to control gas exchange and water loss.

Define pathogen and name the four types.

A pathogen is a microorganism that causes infectious disease. The four types are bacteria, viruses, fungi, and protists.

How do bacteria and viruses make us feel ill (differ in mechanism)?

Bacteria reproduce rapidly and produce toxins that damage tissues and make us feel ill. Viruses live and reproduce inside host cells, causing cell damage when new viruses burst out (lysis).

Give an example disease caused by each pathogen type: virus, bacterium, fungus, protist.

Virus — measles / HIV / tobacco mosaic virus (plants). Bacterium — Salmonella (food poisoning) / gonorrhoea. Fungus — rose black spot. Protist — malaria (spread by mosquito vectors).

State three ways the spread of disease can be reduced.

Good hygiene (e.g. handwashing), isolating infected individuals, destroying vectors, vaccination, and being careful with food/water (e.g. sterilising). Any relevant measures that break the transmission route.

Describe how the human body's non-specific defences prevent pathogens entering.

The skin acts as a barrier and secretes antimicrobial substances; the nose has hairs and mucus to trap particles; the trachea and bronchi produce mucus and have cilia to waft it away; and the stomach produces hydrochloric acid to kill pathogens in food.

Describe the three ways white blood cells defend the body against pathogens.

1) Phagocytosis — engulfing and digesting pathogens. 2) Producing antibodies that bind to specific antigens on pathogens, causing them to clump and be destroyed. 3) Producing antitoxins that neutralise toxins released by pathogens.

What is an antigen and how does it relate to antibodies?

An antigen is a unique molecule (usually a protein) on the surface of a pathogen. Lymphocytes recognise the specific antigen and produce complementary antibodies that bind to it, marking the pathogen for destruction.

How does vaccination make a person immune to a disease?

A vaccine introduces small quantities of dead or inactive pathogens (or their antigens). White blood cells (lymphocytes) respond by producing antibodies and memory cells. If the live pathogen later enters, memory cells produce the correct antibodies quickly and in large amounts, destroying it before illness occurs.

What is herd immunity?

When a large enough proportion of the population is vaccinated (immune), the spread of a pathogen is greatly reduced because there are few susceptible people to infect. This also protects unvaccinated individuals.

Compare the primary and secondary immune responses.

Primary response: on first exposure, antibody production is slow and small, so the person may become ill. Secondary response: on re-exposure, memory cells trigger faster and larger antibody production, destroying the pathogen before symptoms develop — this is immunity.

Write the word and balanced symbol equation for photosynthesis.

Word: carbon dioxide + water $\to$ glucose + oxygen (using light energy). Symbol: $$\ce{6CO2 + 6H2O ->[light] C6H12O6 + 6O2}$$

Is photosynthesis endothermic or exothermic, and why?

Photosynthesis is endothermic because it transfers energy from the environment (light) into the chemical store of glucose — energy is taken in from the surroundings.

Name the three factors that can limit the rate of photosynthesis.

Light intensity, carbon dioxide concentration, and temperature. (Amount of chlorophyll is also a factor.) A limiting factor is the one in shortest supply that restricts the rate.

How does the inverse square law relate light intensity to distance from a lamp?

Light intensity is inversely proportional to the square of the distance from the source: $$\text{light intensity} \propto \frac{1}{d^{2}}$$ So doubling the distance reduces the light intensity to one quarter.

Give four uses of the glucose produced in photosynthesis.

Used in respiration (to release energy); converted to starch for storage; used to make cellulose for cell walls; used to make amino acids/proteins (with nitrate ions); and converted to lipids/oils for storage in seeds.

Write the word and balanced symbol equation for aerobic respiration.

Word: glucose + oxygen $\to$ carbon dioxide + water (+ energy). Symbol: $$\ce{C6H12O6 + 6O2 -> 6CO2 + 6H2O}$$

Compare aerobic and anaerobic respiration, including the products in muscle and yeast.

Aerobic respiration uses oxygen and releases much more energy, producing $\ce{CO2}$ and water. Anaerobic respiration occurs without oxygen and releases less energy: in muscles glucose $\to$ lactic acid; in yeast/plants (fermentation) glucose $\to$ ethanol + carbon dioxide. Respiration is exothermic and happens continuously in living cells.