2nd Year Biology — MCQs & Practice Questions

Homeostasis is the maintenance of a constant internal environment despite changes outside. An example is keeping body temperature (~37 °C), blood glucose, or water balance constant.

It shivers — rapid muscle contractions release heat; the skin blood vessels narrow (vasoconstriction) to reduce heat loss; and hairs stand up to trap an insulating layer of air.

1. Insulin is released when blood glucose is high[1]
2. it makes the liver and muscles take up glucose[1]
3. storing it as glycogen, so blood glucose falls[1]
4. Glucagon is released when blood glucose is low[1]
5. it makes the liver break down glycogen[1]
6. releasing glucose so blood glucose rises[1]

High glucose → insulin → store as glycogen (falls); low glucose → glucagon → release glucose (rises).

The blood flows next to a partially permeable membrane with dialysis fluid on the other side. Urea diffuses out into the fluid because there is none in the fluid (a concentration gradient). Glucose is kept in the dialysis fluid at the same concentration as normal blood, so there is no gradient and glucose does not diffuse out.

1. The rise in glucose is detected by the pancreas[1]
2. which releases insulin[1]
3. insulin makes the liver and muscles take up glucose and store it as glycogen, lowering blood glucose[1]
4. Type 1: the pancreas makes little/no insulin (treated by injection)[1]
5. Type 2: the body no longer responds well to insulin (managed by diet/exercise)[1]

Pancreas detects high glucose → insulin → liver stores glycogen (glucose falls); Type 1 = no insulin made, Type 2 = poor response to insulin.

Any two of: support and shape, protection of vital organs, and making blood cells in the bone marrow.

Cartilage cushions the bone ends and reduces friction; synovial fluid lubricates the joint so it moves smoothly; ligaments hold the bones together.

1. A muscle can only contract (pull), not push[1]
2. so a second muscle is needed to move the bone back[1]
3. To bend the arm the biceps contracts[1]
4. while the triceps relaxes[1]
5. to straighten the arm the triceps contracts[1]
6. while the biceps relaxes[1]

Muscles only pull, so they need a partner; biceps contracts (triceps relaxes) to bend, triceps contracts (biceps relaxes) to straighten.

A broken bone can heal (it grows and repairs), and bone marrow makes blood cells — both show bone has living cells and a blood supply.

1. A muscle can only pull (contract), not push[1]
2. so a second muscle is needed to move the bone back the other way[1]
3. The biceps contracts (triceps relaxes) to bend the arm[1]
4. the triceps contracts (biceps relaxes) to straighten it[1]
5. the elbow joint is the pivot[1]

Muscles only pull, so they need a partner; biceps bends and triceps straightens the forearm, with the elbow as the pivot.

Nervous uses electrical impulses, hormonal uses chemicals; nervous travels along neurones, hormonal in the blood; nervous is fast and brief, hormonal is slower and longer-lasting.

It follows a fixed short pathway (the reflex arc) through the spinal cord, bypassing conscious processing in the brain, so the response is quick and protects the body.

1. It is a reflex action[1]
2. its purpose is to protect the body from harm quickly[1]
3. A receptor in the skin detects the heat and a sensory neurone carries the impulse to the spinal cord[1]
4. a relay neurone passes it on within the spinal cord[1]
5. a motor neurone carries the impulse to the muscle (effector)[1]
6. the muscle contracts to pull the hand away[1]

A protective reflex; receptor → sensory neurone → relay neurone → motor neurone → effector muscle contracts.

The impulse arrives at the end of the first neurone and triggers the release of a neurotransmitter chemical. This diffuses across the synapse gap and binds to receptors on the next neurone, setting off a new impulse in it.

In bright light, circular muscles in the iris contract to make the pupil smaller, letting in less light. This protects the light-sensitive retina from damage by too much light.

1. Sensory neurone (receptor to CNS)[1]
2. motor neurone (CNS to effector)[1]
3. Only the end of one neurone releases neurotransmitter[1]
4. and only the next neurone has receptors for it[1]
5. so the signal can only pass from the first neurone to the second, not backwards[1]

Sensory = receptor→CNS, motor = CNS→effector; a synapse is one-way because only one side releases transmitter and only the other has receptors.

Innate behaviour is inherited and present from birth and is the same in all members of the species; learned behaviour develops through experience and varies between individuals.

1. Innate behaviour is inherited and present from birth, needing no learning[1]
2. e.g. a reflex or an instinct such as web-spinning[1]
3. Conditioning — linking a response to a new stimulus[1]
4. e.g. Pavlov's dogs salivating at a bell[1]
5. Imprinting — a young animal bonding to the first moving object it sees[1]
6. e.g. a duckling following its mother (or habituation / trial-and-error with an example)[1]

Innate = inborn, no learning (e.g. reflex/instinct); learned examples: conditioning (Pavlov's dogs) and imprinting (ducklings).

Communication lets animals coordinate behaviour — warning of danger, attracting a mate, or organising a group. For example, birds use alarm calls (sound) to warn others of a predator (or bees 'dance' to show where food is).

1. Safety in numbers / better defence against predators[1]
2. cooperative hunting or easier mate-finding[1]
3. Migration takes the animal to a better climate or feeding ground[1]
4. so it avoids the harsh season and finds food[1]
5. Hibernation lowers metabolism to save energy when food is scarce in winter[1]

Group living: safety and cooperation; migration escapes to food/better climate; hibernation saves energy through scarce winters.

Asexual needs one parent, sexual needs two; asexual has no gametes, sexual involves gamete fusion; asexual offspring are identical (clones), sexual offspring are genetically varied.

Variation means offspring differ, so if the environment changes some are more likely to have features that let them survive and reproduce, helping the species adapt.

1. At ovulation an egg is released from the ovary[1]
2. the egg travels into the oviduct[1]
3. the uterus lining thickens ready to receive an embryo[1]
4. If fertilised, the embryo implants in the lining[1]
5. and develops into a fetus[1]
6. if not fertilised, the lining breaks down and is lost as the period[1]

Ovulation releases an egg and the lining thickens; if fertilised the embryo implants and develops, if not the lining is shed as the period.

Oestrogen rebuilds the uterus lining and leads to ovulation; progesterone maintains the thickened lining ready for pregnancy, and its fall causes the lining to break down.

1. FSH stimulates an egg to mature[1]
2. LH triggers ovulation (release of the egg)[1]
3. The pill contains hormones (e.g. oestrogen/progesterone)[1]
4. that prevent an egg from maturing or being released (no ovulation)[1]
5. so there is no egg to be fertilised[1]

FSH matures the egg, LH triggers ovulation; the pill's hormones stop ovulation, so no egg is released to be fertilised.

Growth is a permanent increase in size (more cells and material). Development is the change in form and complexity as the organism matures, including the differentiation of cells into specialised types.

1. The zygote divides repeatedly by mitosis to form an embryo[1]
2. the cells differentiate into specialised tissues and organs[1]
3. the embryo grows into a fetus that develops until birth[1]
4. Plant growth occurs at meristems (shoot and root tips)[1]
5. where cells divide by mitosis[1]
6. then enlarge and differentiate into specialised tissues[1]

Zygote → mitosis → embryo → differentiation into tissues/organs → fetus; plants grow at meristems by division, enlargement and differentiation.

Percentage growth = (increase ÷ original) × 100 = (6 ÷ 20) × 100 = 30%.

1. Complete metamorphosis has very different stages: egg, larva, pupa, adult[1]
2. e.g. a butterfly or beetle[1]
3. Incomplete metamorphosis: the young (nymphs) resemble small adults and change gradually[1]
4. e.g. a locust or grasshopper[1]
5. Advantage: larvae and adults eat different foods, so they do not compete[1]

Complete = egg/larva/pupa/adult (butterfly); incomplete = nymphs like small adults, gradual (locust); complete lets young and adults avoid competing for food.

DNA is a double helix of two strands. Each strand is made of nucleotides (sugar, phosphate and a base). The strands are held together by base pairs, with adenine pairing with thymine and guanine with cytosine.

1. The DNA double helix unzips as the base pairs separate[1]
2. each old strand acts as a template[1]
3. free nucleotides pair against it (A–T, G–C) forming two identical molecules[1]
4. Each triplet of three bases codes for one amino acid[1]
5. the gene is copied into RNA and read at a ribosome[1]
6. amino acids are joined in the order set by the bases, giving the protein its structure[1]

Replication: unzip, template, pair nucleotides (semi-conservative); protein: triplets code amino acids, transcribed to RNA, translated at a ribosome.

Enzymes cut DNA at specific base sequences, so the desired gene can be cut out of one organism's DNA and (using enzymes to join it) inserted into another organism's DNA, which then expresses the gene.

1. PCR makes many copies of a small DNA sample[1]
2. used in forensics / DNA profiling / research (any one)[1]
3. Benefit: it can detect disorder-causing alleles early[1]
4. allowing treatment, informed choices or genetic counselling[1]
5. Concern: privacy of the information / possible misuse (e.g. by insurers) / difficult decisions[1]

PCR amplifies DNA (used in forensics); screening detects disorders early (benefit) but raises privacy/misuse concerns.

Mitosis makes 2 cells, meiosis makes 4; mitosis keeps the chromosome number the same (diploid), meiosis halves it (haploid); mitosis gives identical cells, meiosis gives genetically different cells.

Mitosis produces genetically identical cells for growth (increasing cell number) and for the repair and replacement of damaged or worn-out tissue.

1. 46 chromosomes[1]
2. mitosis copies the DNA and gives each cell an identical full (diploid) set[1]
3. 23 chromosomes in a gamete[1]
4. meiosis halves the number to make haploid gametes[1]
5. so that fertilisation does not double the number each generation[1]
6. Fertilisation restores the diploid number (46)[1]

Mitosis → 46 (identical diploid); gametes → 23 (meiosis halves it so fertilisation keeps 46 constant); fertilisation restores the diploid number.

A diploid cell has the full set of chromosomes in matching pairs (46 in humans); a haploid cell has only one chromosome of each pair (23 in humans), as in gametes.

Stem cells are unspecialised and can divide and differentiate into many cell types, so they could be used to replace damaged or diseased tissue (for example nerve or blood cells). A concern is the ethical objection to using embryonic stem cells (or risks such as rejection or uncontrolled division).

1. Growth (increasing the number of cells)[1]
2. repair/replacement of damaged or worn-out tissue (or asexual reproduction)[1]
3. Meiosis halves the chromosome number to make haploid gametes[1]
4. so that at fertilisation the two gametes restore the normal diploid number[1]
5. if gametes were diploid, the chromosome number would double each generation[1]

Mitosis: growth and repair; gametes need meiosis to halve the number so fertilisation restores the diploid number.

Allele: a version of a gene. Genotype: the alleles an organism carries. Phenotype: the characteristic actually shown by the organism.

The mother's egg always carries an X chromosome; the father's sperm carries either an X or a Y. If an X sperm fertilises the egg the child is XX (female); if a Y sperm does, the child is XY (male) — a 50:50 chance.

1. The man is Bb (heterozygous brown)[1]
2. the woman is bb (blue, homozygous recessive)[1]
3. Man's gametes B and b; woman's gametes b and b[1]
4. Offspring: Bb, Bb, bb, bb[1]
5. genotypes 2 Bb : 2 bb[1]
6. phenotype ratio 1 brown : 1 blue (50%)[1]

Parents Bb × bb; offspring 2 Bb : 2 bb = 1 brown : 1 blue.

A dominant allele is expressed even when paired with a recessive one, so only it shows. Codominant alleles are both expressed together in the heterozygote, so both features appear (as in blood group AB).

1. A child with cystic fibrosis is ff (homozygous recessive)[1]
2. a carrier is Ff (heterozygous)[1]
3. Parents Ff × Ff; gametes F and f from each[1]
4. Offspring: FF, Ff, Ff, ff[1]
5. genotypes 1 FF : 2 Ff : 1 ff[1]
6. probability of cystic fibrosis (ff) = 1 in 4 (25%)[1]

Affected = ff, carrier = Ff; Ff × Ff gives 1 FF : 2 Ff : 1 ff, so a 1 in 4 chance of cystic fibrosis.

Genetic variation is inherited and arises from mutation and gene shuffling (e.g. blood group); environmental variation is caused by surroundings and is not inherited (e.g. a scar, or a plant made small by poor soil).

1. There is variation among individuals of a species[1]
2. more offspring are produced than can survive, so there is competition[1]
3. individuals better adapted are more likely to survive and reproduce[1]
4. they pass on their advantageous alleles, so over generations these become more common[1]
5. Only genetic variation is inherited / passed to offspring[1]
6. environmental variation is not passed on, so it cannot change the population over generations[1]

Natural selection: variation → overproduction/competition → best-adapted survive and reproduce → alleles become more common; only genetic variation is heritable, so only it drives evolution.

Farmers select the wheat plants with the highest grain yield and breed them together. Their offspring inherit the high-yield alleles; repeating this over many generations steadily increases the yield of the crop.

1. There is variation: some individuals carry an allele giving resistance[1]
2. when the poison is applied, the non-resistant individuals die[1]
3. the resistant ones survive and reproduce[1]
4. passing on the resistance allele, so the population becomes resistant[1]
5. Two isolated populations cannot interbreed[1]
6. and diverge under different mutations/selection until they can no longer breed to give fertile offspring — separate species[1]

Resistant variants survive the poison and reproduce, spreading the allele; isolated populations diverge until they can't interbreed — new species.

Yeast ferments sugars, producing ethanol and carbon dioxide. In brewing the ethanol makes the alcoholic drink; in bread-making the carbon dioxide is trapped in the dough and makes it rise.

Benefit: it produces cheap, pure medicines such as human insulin (or pest-resistant crops). Concern: possible safety, ethical or ecological risks. Product: human insulin.

1. The human insulin gene is cut out of human DNA using enzymes[1]
2. it is inserted into the DNA of a bacterium[1]
3. the bacteria are grown in large numbers in a fermenter[1]
4. the insulin they make is collected and purified[1]
5. It produces pure human insulin (fewer allergic reactions)[1]
6. in large amounts, cheaply and reliably[1]

Cut out the insulin gene, insert it into bacteria, grow them in a fermenter, purify the insulin; advantages: pure human insulin, cheap and plentiful.

Temperature — kept at the optimum for the microbe's enzymes (and cooled to remove respiration heat); pH — kept optimal so the enzymes work; sterility — to stop contamination by unwanted microbes. (Oxygen/nutrient supply and stirring are also valid.)

1. A GM crop has had a gene from another organism inserted into its DNA[1]
2. so it gains a useful characteristic[1]
3. e.g. resistance to pests, higher yield or added nutrients[1]
4. Benefit: more or better food / medicines produced[1]
5. Concern: possible effects on health or ecosystems, or ethical objections[1]

A GM crop carries an inserted gene for a useful trait (e.g. pest resistance); benefit = better food/yield, concern = health/ecological/ethical risks.

Energy is lost (about 90%) at each trophic level, so less energy is available higher up the chain. Less energy supports less living mass, so top predators are far fewer than producers.

Photosynthesis removes carbon dioxide from the air and fixes it into glucose; respiration (and combustion) returns carbon dioxide to the air; decomposers break down dead organisms, releasing their carbon back as carbon dioxide.

1. Grass is the producer[1]
2. the rabbit is the primary consumer (herbivore)[1]
3. the fox is the secondary consumer (carnivore)[1]
4. Energy is lost at each level[1]
5. in respiration, movement, heat and undigested waste[1]
6. so only about 10% passes on, and the chain cannot support many more levels[1]

Grass = producer, rabbit = primary consumer, fox = secondary consumer; ~90% of energy is lost at each step, so little reaches the top.

Any three: a shortage of food, water or space; an increase in predators (e.g. foxes); the spread of disease; or increased competition.

1. Energy is lost at each level as heat from respiration[1]
2. in movement and in undigested waste[1]
3. so only about 10% is passed on to the next level[1]
4. A pyramid of biomass accounts for the size/mass of organisms, not just their number[1]
5. so it is always a true pyramid, unlike numbers (where one large producer can support many consumers)[1]

~90% of energy is lost (respiration, movement, waste), so ~10% passes on; biomass pyramids reflect mass so they always taper, unlike number pyramids.