9th Class Biology — MCQs & Practice Questions

Any four of: movement, respiration, sensitivity, growth, reproduction, excretion, nutrition.

Independent variable: the factor deliberately changed. Dependent variable: the factor measured in response. Controlled variable: a factor kept constant so it does not affect the result.

1. Hypothesis: dough rises faster at higher temperatures (up to an optimum)[1]
2. Independent variable: temperature[1]
3. Dependent variable: rise in height (or volume) in a fixed time[1]
4. Keep controlled variables constant: same dough recipe, mass, container, time[1]
5. Measure the rise for each temperature[1]
6. Repeat each temperature several times and average for reliability[1]

Hypothesis that warmth speeds rising; IV = temperature, DV = rise; keep recipe/mass/time constant and repeat for reliability.

Actual size = image size ÷ magnification = 40 ÷ 2000 = 0.02 mm.

Advantage: it magnifies far more and shows much finer detail (higher resolution). Limitation: it cannot be used on living specimens, which must be dead and specially prepared.

1. Independent variable: the concentration of caffeine[1]
2. dependent variable: the heart rate of the water flea[1]
3. Control the temperature[1]
4. and the size/age of the water fleas (or same species)[1]
5. Repeating gives an average and reduces the effect of random error, improving reliability[1]

IV = caffeine concentration, DV = heart rate; control temperature and flea size; repeat for a reliable average.

Two Latin words: the genus first (capital letter) and the species second (lower case); the whole name is italicised (or underlined), e.g. Homo sapiens.

Any three, e.g. Prokaryotae — no nucleus; Plantae — photosynthesise; Animalia — multicellular, feed on other organisms; Fungi — absorb nutrients, chitin walls.

1. A group of similar organisms[1]
2. that can breed together to produce fertile offspring[1]
3. Kingdom, phylum, class, order,[1]
4. family, genus, species[1]
5. Each species has one unique, universal name[1]
6. understood worldwide, avoiding the ambiguity of common names[1]

Species = organisms that interbreed to give fertile offspring; hierarchy kingdom→…→species; binomial names are unique and universal.

A dichotomous key is a set of paired statements or questions, each offering two choices about an observable feature. At each step you pick the option that matches the organism, which directs you to the next pair, until you reach the organism's name.

For example a cactus: a thick waxy cuticle to reduce water loss, and spines (reduced leaves) that lower water loss and deter herbivores. (Any organism with two valid habitat adaptations is acceptable.)

1. To identify organisms and organise the diversity of life[1]
2. and to study their relationships / shared ancestry[1]
3. A binomial name is unique to one species[1]
4. and is understood worldwide, avoiding the ambiguity of common names[1]
5. Species[1]

Classify to identify/organise and show relationships; binomial names are unique and universal; the smallest group is the species.

Cell wall — support and shape (cellulose); chloroplasts — photosynthesis; large permanent vacuole — stores cell sap and keeps the cell turgid.

Diffusion is the passive net movement of particles from high to low concentration (no energy needed). Active transport moves particles against the gradient, from low to high concentration, and needs energy from respiration.

1. Osmosis is the movement of water[1]
2. across a partially permeable membrane from a dilute to a more concentrated solution[1]
3. In pure water the cube gains mass[1]
4. because water enters the cells by osmosis (cells more concentrated than pure water)[1]
5. In concentrated sugar solution the cube loses mass[1]
6. because water leaves the cells by osmosis toward the more concentrated solution[1]

Osmosis = water moving across a partially permeable membrane to the more concentrated side; cube gains mass in water, loses mass in concentrated sugar.

Diffusion only moves substances down a concentration gradient (high to low) and needs no energy. Active transport uses energy from respiration to move substances against the gradient, from low to high concentration.

A cell wall and chloroplasts (also a large permanent vacuole). The cell wall (cellulose) supports and shapes the cell; chloroplasts carry out photosynthesis; the vacuole stores cell sap and keeps the cell turgid.

1. Osmosis[1]
2. In pure water the solution is more dilute than the cell contents[1]
3. so water enters the cells by osmosis and the mass increases[1]
4. In a concentrated solution the outside is more concentrated than the cells[1]
5. so water leaves the cells by osmosis and the mass decreases[1]

Osmosis; gains mass in water (water enters), loses mass in concentrated solution (water leaves).

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.

Cell → tissue → organ → organ system → organism.

A biconcave disc gives a large surface area for absorbing oxygen; it is packed with haemoglobin to carry oxygen; and it has no nucleus, leaving more room for haemoglobin.

1. A cell whose structure/shape[1]
2. is adapted to carry out one particular function[1]
3. Nerve cell — long and thin to carry impulses[1]
4. (valid adaptation)[1]
5. Root hair cell — long extension for a large absorbing area[1]
6. (or red blood cell — biconcave/haemoglobin)[1]

A specialised cell is shaped for one job; e.g. nerve cell (long, carries impulses) and root hair cell (large area, absorbs water).

Stem cells are unspecialised and can keep dividing; their daughter cells differentiate into the specialised cells a tissue needs, allowing the organism to grow and to repair or replace damaged tissue.

The digestive system breaks the food into small soluble molecules and absorbs them; the circulatory system carries these nutrients (and oxygen) to the cells; the respiratory system supplies the oxygen needed to release the food's energy in respiration.

1. Cell → tissue → organ[1]
2. → organ system → organism[1]
3. Different cells become specialised for particular jobs[1]
4. each doing its task efficiently[1]
5. so the organism as a whole can do far more than a single unspecialised cell could[1]

Cell→tissue→organ→organ system→organism; specialisation (division of labour) lets each cell do its job efficiently so the organism achieves more.

Starch: add iodine solution — a blue-black colour is positive. Reducing sugar: warm with Benedict's solution — a change from blue to a brick-red precipitate is positive.

A protein's function depends on its specific 3-D shape (e.g. an enzyme's active site). Strong heating denatures it — changes its shape — so it can no longer carry out its function.

1. Carbohydrate monomer: a monosaccharide (e.g. glucose)[1]
2. Protein monomer: an amino acid[1]
3. Condensation joins monomers and releases water[1]
4. hydrolysis splits polymers by adding water[1]
5. Lipids store energy / insulate the body[1]
6. cushion organs / form cell membranes (any two)[1]

Carbohydrate monomer = monosaccharide, protein monomer = amino acid; condensation joins (releases water), hydrolysis splits (adds water); lipids store energy, insulate, cushion and build membranes.

It is a good solvent, so reactions occur in solution and substances are transported dissolved in it; and it has a high heat capacity, so it resists temperature change and helps keep organisms at a steady temperature.

Lipids contain about twice as much energy per gram as carbohydrates, so they store a lot of energy compactly for the long term (and also insulate). Carbohydrates like glucose are soluble and quickly broken down, making them ideal for immediate, short-term energy.

1. Reducing sugar: warm with Benedict's solution[1]
2. a positive result is blue changing to a brick-red precipitate[1]
3. Protein: add biuret solution[1]
4. a positive result is blue changing to purple[1]
5. Iodine blue-black shows starch is present[1]
6. starch is an insoluble energy store, so it does not affect the cell's water balance[1]

Benedict's (blue→brick-red) for reducing sugar; biuret (blue→purple) for protein; iodine blue-black shows starch, a compact insoluble store.

An enzyme has a specifically shaped active site. Only a substrate whose shape is complementary to the active site can fit and bind, forming an enzyme–substrate complex. Because only one substrate fits, the enzyme catalyses only that one reaction.

High temperature breaks the bonds that hold the enzyme's 3-D shape, denaturing it. The active site changes shape so the substrate can no longer bind, and the reaction almost stops.

1. As pH rises toward the optimum, the rate increases[1]
2. conditions increasingly suit the enzyme's active site[1]
3. Beyond the optimum the rate falls[1]
4. the enzyme is denatured — the active site changes shape and substrate no longer binds[1]
5. Temperature[1]
6. substrate (or enzyme) concentration[1]

Rate rises to an optimum pH then falls as the enzyme denatures; other factors: temperature and substrate/enzyme concentration.

Amylase digests starch (carbohydrate) to sugars; protease digests protein to amino acids; lipase digests fats to fatty acids and glycerol.

Cooling gives particles less kinetic energy, so there are fewer, less energetic collisions between enzyme and substrate — the reaction slows. But it does not break the bonds holding the enzyme's shape, so the active site is unchanged and the enzyme works normally again when warmed.

1. As temperature rises to the optimum, the rate (gas produced) increases[1]
2. molecules have more kinetic energy and collide more often[1]
3. so more enzyme–substrate complexes form[1]
4. Above the optimum the rate falls sharply[1]
5. the heat breaks the bonds holding the enzyme's shape (denaturing)[1]
6. the active site changes shape so the substrate no longer fits and the reaction stops[1]

Rate rises to an optimum (more successful collisions), then falls as the enzyme denatures and its active site is destroyed.

Glucose + oxygen → carbon dioxide + water (+ energy). Most aerobic respiration occurs in the mitochondria.

Aerobic uses oxygen, releases a lot of energy, and gives carbon dioxide and water. Anaerobic uses no oxygen, releases little energy, and gives lactic acid.

1. Light intensity[1]
2. carbon dioxide concentration[1]
3. temperature[1]
4. Increasing light increases the rate[1]
5. while light is the limiting factor[1]
6. it levels off when another factor (CO₂ or temperature) becomes limiting[1]

Limiting factors: light, CO₂, temperature; rate rises with light then plateaus when another factor limits it.

Boil the leaf to kill it, then decolourise it in hot ethanol (away from a flame) and rinse it. Add iodine solution: a blue-black colour shows starch has been made, indicating photosynthesis.

Being thin gives a short diffusion distance so gases and light reach the inner cells quickly; the many stomata allow carbon dioxide to diffuse in (and oxygen out) fast enough for photosynthesis.

1. Carbon dioxide + water → glucose + oxygen (light energy, chlorophyll)[1]
2. Light intensity[1]
3. carbon dioxide concentration[1]
4. temperature[1]
5. As light increases the rate rises (light is limiting)[1]
6. then levels off when another factor becomes limiting[1]

CO₂ + water → glucose + oxygen; limiting factors light/CO₂/temperature; rate rises with light then plateaus when another factor limits it.

Xylem carries water and minerals upward in dead tubes; phloem carries dissolved food (sucrose) in living cells, in both directions.

Higher temperature and wind speed evaporation, and dry air gives a steeper water-vapour gradient out of the leaf, so more water is lost. On a cool, still, humid day all these are reduced.

1. Transpiration is the loss of water vapour from a plant[1]
2. mostly through the stomata[1]
3. Wind increases the rate[1]
4. it removes water vapour, keeping a steep gradient so evaporation continues[1]
5. Nitrate (or magnesium)[1]
6. for proteins (or chlorophyll)[1]

Transpiration = water-vapour loss via stomata; wind speeds it; nitrate is needed for proteins (magnesium for chlorophyll).

The cells lose water and become flaccid, so they lose their turgor pressure. Without turgor to support them, the stems and leaves droop — the plant wilts.

The moving air blows away water vapour from around the leaves, keeping a steep water-vapour gradient, so transpiration (and therefore water uptake) speeds up.

1. Water enters root hair cells by osmosis[1]
2. it travels up the xylem[1]
3. in the transpiration stream, pulled up as water evaporates from the leaves[1]
4. Higher temperature (or lower humidity)[1]
5. more wind (or brighter light)[1]

Water enters roots by osmosis, rises in the xylem (transpiration stream); faster in warm, dry, windy or bright conditions.

Bright/scented petals attract insects; nectar draws them in; sticky pollen and a sticky stigma ensure pollen sticks to and is transferred by the insect.

Water, oxygen and a suitable temperature. Oxygen is needed for aerobic respiration, which releases the energy the seedling needs.

1. After pollination a pollen tube grows down the style[1]
2. to reach the ovule in the ovary[1]
3. the male nucleus fuses with the female nucleus[1]
4. Dispersal spreads seeds from the parent[1]
5. reducing competition for light, water and minerals[1]
6. methods: wind and animals (also water)[1]

A pollen tube grows to the ovule and nuclei fuse; dispersal (wind, animals, water) reduces competition.

It is brightly coloured and tasty so animals eat it; the seeds have tough coats that survive digestion and are deposited, in droppings, far from the parent plant.

Advantage: it is fast and needs no mate or pollinator, and the offspring are identical to a successful parent. Disadvantage: there is no genetic variation, so the whole population is vulnerable if the environment changes or a disease strikes.

1. Sexual needs two parents/gametes; asexual needs one parent[1]
2. sexual gives varied offspring; asexual gives identical offspring[1]
3. They should use asexual reproduction (e.g. cuttings)[1]
4. because it produces genetically identical offspring (clones)[1]
5. so every new plant has the same prized characteristics as the parent[1]

Sexual: two parents, varied offspring; asexual: one parent, identical offspring; use cuttings (asexual) to get identical copies of the prize plant.