Cambridge IGCSE Biology (0610) Syllabus

What is an enzyme?

A biological catalyst, made of protein, that speeds up the rate of a chemical reaction without being used up (lowering the activation energy).

Explain how temperature affects enzyme activity, including denaturation.

Rate increases with temperature up to an optimum; above this the enzyme's active site changes shape (denatures), so the substrate no longer fits and the reaction rate falls.

Why is enzyme action described as specific (lock and key)?

Each enzyme's active site has a complementary shape to only one substrate, so it catalyses only one reaction.

Write the word and balanced chemical equation for photosynthesis.

Carbon dioxide + water $\xrightarrow{\text{light, chlorophyll}}$ glucose + oxygen. $$\ce{6CO2 + 6H2O ->[light][chlorophyll] C6H12O6 + 6O2}$$

Name the three limiting factors of photosynthesis.

Light intensity, carbon dioxide concentration, and temperature.

What is the role of chlorophyll in photosynthesis?

It absorbs light energy and transfers it to chemical energy in molecules used to make glucose.

Name the four main types of human teeth and the function of incisors and canines.

Incisors, canines, premolars and molars. Incisors bite/cut food; canines tear food.

State the role of the enzyme amylase and where it is produced.

Amylase breaks down starch into maltose; it is produced in the salivary glands and the pancreas.

What is the function of bile, and where is it made and stored?

Bile emulsifies fats (increasing surface area for lipase) and neutralises stomach acid; it is made in the liver and stored in the gall bladder.

How are villi adapted for absorption in the small intestine?

They are numerous and have microvilli (large surface area), thin walls (short diffusion distance), a good blood supply, and lacteals to absorb fats.

Define a balanced diet and name a deficiency disease of vitamin C and of iron.

A balanced diet contains all nutrients in the correct amounts/proportions. Lack of vitamin C causes scurvy; lack of iron causes anaemia.

Name the two main transport tissues in plants and what each transports.

Xylem transports water and mineral ions from roots to leaves; phloem transports sucrose and amino acids (assimilates) around the plant.

Define transpiration.

The loss of water vapour from plant leaves by evaporation of water at the surfaces of the mesophyll cells, followed by diffusion of water vapour through the stomata.

State three factors that increase the rate of transpiration.

Increased temperature, increased wind/air movement, increased light intensity, and decreased humidity.

How are root hair cells adapted for water uptake?

They have a long, thin extension giving a large surface area, and a thin cell wall/membrane, increasing the rate of water absorption by osmosis.

Describe the double circulation of the human heart.

Blood passes through the heart twice per circuit: a pulmonary circuit to the lungs and back, and a systemic circuit to the rest of the body and back.

Compare the structure of arteries and veins.

Arteries have thick muscular/elastic walls, a narrow lumen and no valves (carry blood at high pressure away from heart); veins have thin walls, a wide lumen and valves (carry blood at low pressure towards heart).

List the four components of blood and one function of each.

Red blood cells (carry oxygen as oxyhaemoglobin), white blood cells (defence/immunity), platelets (clotting), and plasma (transports dissolved substances, e.g. CO2, nutrients, hormones).

How are red blood cells adapted to their function?

Biconcave shape (large surface area for gas exchange), no nucleus (more room for haemoglobin), and contain haemoglobin to bind oxygen.

Name, in order, the blood vessels that connect the heart to the lungs and back.

The pulmonary artery carries deoxygenated blood from the heart to the lungs; the pulmonary vein returns oxygenated blood from the lungs to the heart.

Write the word and balanced equation for aerobic respiration.

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

Write the word equation for anaerobic respiration in human muscle and in yeast.

In muscle: glucose $\to$ lactic acid (+ energy). In yeast: glucose $\to$ alcohol (ethanol) + carbon dioxide (+ energy).

Why does aerobic respiration release more energy than anaerobic respiration?

Aerobic respiration completely breaks down glucose, while anaerobic respiration only partially breaks it down, leaving energy stored in lactic acid or ethanol.

How are alveoli adapted for efficient gas exchange?

Large surface area (many alveoli), thin walls (one cell thick, short diffusion distance), moist surface, and a rich blood capillary supply maintaining a concentration gradient.

State the function of the kidneys in excretion.

They remove urea and excess water and salts from the blood, forming urine, and help regulate water and ion content (osmoregulation).

Define homeostasis.

The maintenance of a constant internal environment despite changes in external conditions.

Describe how the body responds to a rise in body temperature (above normal).

Vasodilation of skin arterioles increases blood flow to the surface, and sweat glands produce sweat that evaporates, both increasing heat loss to cool the body.

Define a reflex action and give the order of components in a reflex arc.

A reflex action is a rapid, automatic response not involving conscious thought. Pathway: stimulus → receptor → sensory neurone → relay neurone → motor neurone → effector → response.

Compare nervous and hormonal coordination.

Nervous: electrical impulses along neurones, fast, short-lived, very localised effect. Hormonal: chemicals in the blood, slower, longer-lasting, can be widespread.

State the role of insulin and glucagon in blood glucose regulation.

Insulin lowers blood glucose by stimulating cells to take up glucose and the liver to store it as glycogen; glucagon raises blood glucose by converting glycogen back to glucose.

Define a gene and an allele.

A gene is a length of DNA that codes for a protein (a unit of inheritance). An allele is an alternative form (version) of a gene.

What is the structure of DNA?

A double helix of two strands held together by complementary base pairs: adenine (A) with thymine (T), and cytosine (C) with guanine (G).

Distinguish between genotype and phenotype, and between homozygous and heterozygous.

Genotype is the genetic makeup (alleles); phenotype is the observable features. Homozygous has two identical alleles of a gene; heterozygous has two different alleles.

In a monohybrid cross between two heterozygous parents (Tt × Tt), what is the expected phenotype ratio?

3 dominant : 1 recessive ($3:1$).

Distinguish between continuous and discontinuous variation, giving an example of each.

Continuous variation shows a range of values (e.g. height), influenced by genes and environment. Discontinuous variation shows distinct categories (e.g. blood group, tongue rolling), controlled by genes alone.

Define natural selection.

The process where organisms better adapted to their environment survive and reproduce, passing on the alleles for their advantageous characteristics to the next generation.

What is a mutation and why is it important for variation?

A mutation is a random genetic change in a gene or chromosome; it is the original source of new alleles and therefore new variation.

Define producer, consumer, herbivore and carnivore.

Producer: an organism (usually a plant) that makes its own organic molecules from inorganic ones, usually by photosynthesis. Consumer: an organism that gets energy by feeding on others. Herbivore: eats plants. Carnivore: eats other animals.

Why are food chains usually limited to four or five trophic levels?

Energy is lost at each trophic level (through respiration, movement, heat and undigested waste), so there is insufficient energy to support many levels.

Define the term trophic level and what a pyramid of energy shows.

A trophic level is the position of an organism in a food chain/web. A pyramid of energy shows the energy in each trophic level over a given area/time, always decreasing up the levels.

Describe the carbon cycle in terms of the main processes that add and remove atmospheric CO2.

CO2 is removed by photosynthesis; it is added by respiration, combustion (burning) of fossil fuels and wood, and decomposition of dead organisms.

State the roles of bacteria in the nitrogen cycle.

Decomposers/nitrifying bacteria convert proteins to ammonium then to nitrates; nitrogen-fixing bacteria convert nitrogen gas to nitrogen compounds; denitrifying bacteria convert nitrates back to nitrogen gas.

Explain how eutrophication leads to the death of fish in a river.

Excess nitrates/fertilisers cause rapid algal growth (algal bloom); algae die and aerobic bacteria decompose them, using up dissolved oxygen, so aquatic organisms suffocate and die.

Describe two effects of deforestation on the environment.

It reduces biodiversity/habitat loss and disrupts food chains; it increases atmospheric CO2 (less photosynthesis), causes soil erosion, flooding and disturbs the water cycle.

Name two greenhouse gases and one consequence of the enhanced greenhouse effect.

Carbon dioxide and methane. A consequence is global warming / climate change, leading to rising sea levels, ice melting and changed weather patterns.

Why is yeast used in the brewing and baking industries?

Yeast carries out anaerobic respiration (fermentation): producing ethanol (used in brewing) and carbon dioxide (which makes bread dough rise).

Why are bacteria useful in biotechnology and genetic engineering?

They reproduce rapidly, have few ethical concerns, contain plasmids that can take up genes, and lack a membrane-bound nucleus, making genetic manipulation easier.

Outline the main steps in genetically engineering bacteria to produce human insulin.

Cut the human insulin gene out using restriction enzymes; insert it into a bacterial plasmid (vector) using ligase; return the plasmid to the bacterium; the bacterium multiplies and expresses the gene to produce insulin.

Define genetic modification (genetic engineering).

Changing the genetic material of an organism by removing, changing or inserting individual genes (often from another organism) to give the organism a desired characteristic.