10th Class Biology — MCQs & Practice Questions

There are millions of alveoli giving a large surface area; their walls are one cell thick for a short diffusion distance; they have a moist lining so gases dissolve; and they are surrounded by many capillaries that keep the concentration gradient steep.

Breathing is the physical movement of air in and out of the lungs (ventilation). Respiration is the chemical process in cells that releases energy from glucose. Breathing supplies the oxygen respiration needs.

1. Trachea → bronchi → bronchioles[1]
2. → alveoli[1]
3. The diaphragm and intercostal muscles contract[1]
4. the diaphragm flattens and the ribcage moves up and out[1]
5. so the volume of the chest increases and the pressure inside falls[1]
6. air moves in from the higher outside pressure to the lower pressure in the lungs[1]

Trachea → bronchi → bronchioles → alveoli; muscles contract, chest volume rises, internal pressure falls, so air flows in.

During hard exercise the muscles respire anaerobically and build up lactic acid. Extra oxygen (the oxygen debt) is needed afterwards to break down this lactic acid, so deep breathing continues until it is cleared.

Tar contains carcinogens that cause lung cancer; tar paralyses the cilia so mucus and dirt build up, causing infection; and the alveoli walls break down (emphysema), reducing the surface area for gas exchange. (Carbon monoxide also reduces oxygen transport.)

1. A large surface area (millions of alveoli)[1]
2. walls one cell thick for a short diffusion distance[1]
3. a moist lining and a rich capillary blood supply (steep gradient)[1]
4. Carbon monoxide binds to haemoglobin in red blood cells[1]
5. taking the place of oxygen, so the blood carries less oxygen[1]

Alveoli: large area, thin walls, moist lining, rich blood supply; CO binds haemoglobin, cutting oxygen transport.

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.

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.

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.

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.

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.

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.

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.

A cold is caused by a virus, and antibiotics only kill bacteria, so they would have no effect. Using them unnecessarily also helps breed antibiotic-resistant bacteria.

When antibiotics are used, any bacteria with resistance survive and reproduce, passing on the resistance, so resistant strains spread. It can be reduced by not over-prescribing antibiotics and by patients finishing the full course.

1. A depressant slows down the nervous system[1]
2. e.g. alcohol[1]
3. a stimulant speeds up the nervous system[1]
4. e.g. nicotine (in tobacco)[1]
5. Tobacco damages the lungs / causes lung cancer[1]
6. and is addictive (also raises heart disease risk)[1]

Depressant slows the nervous system (alcohol); stimulant speeds it up (nicotine); smoking damages the lungs, causes cancer and is addictive.

Small-scale testing first checks that the drug is safe and finds the correct dose, with fewer people at risk. Only once it is shown to be safe is it given to large groups to test how effective it is.

1. The vaccine contains a weakened/dead pathogen (or part of it)[1]
2. this triggers the immune system to respond[1]
3. producing antibodies and memory cells[1]
4. so if the real pathogen invades later, the memory cells respond quickly and destroy it before illness develops[1]
5. Herd immunity is when enough people are immune that the disease cannot spread easily[1]
6. protecting even those who cannot be vaccinated[1]

A vaccine exposes the immune system to a harmless form, making antibodies and memory cells for a fast future response; herd immunity stops spread when most are immune.