Biology

(b) Nucleus

Robert Brown discovered the nucleus in 1831 while studying orchid cells. Robert Hooke discovered the cell.

(d) ATP

Mitochondria carry out aerobic respiration and produce most of the cell's ATP, the energy currency, so they are called the powerhouse of the cell.

(c) Interphase

Interphase (G1, S and G2) is the longest phase of the cell cycle, as the cell grows and replicates its DNA. Mitosis itself is short.

(d) plantae

Multicellular organisms that make food by photosynthesis are placed in kingdom Plantae.

(b) Protista

Kingdom Protista contains unicellular eukaryotes such as Amoeba and Paramecium. Monera is prokaryotic.

(c) Entomophily

Entomophily is pollination by insects. Malacophily is by snails, chiropterophily by bats and ornithophily by birds.

(d) Plant anatomy

Plant anatomy is the study of the internal structure of plants, such as tissues and tissue systems.

(d) Adenine, Guanine, Cytosine and Thymine

DNA contains A, G, C and T. Uracil replaces thymine in RNA.

(c) Oxides of nitrogen and sulphur

$\mathrm{SO_2}$ and $\mathrm{NO_x}$ dissolve in rain water to form sulphuric and nitric acids, causing acid rain.

(c) Oryza sativa

Triticum aestivum is wheat, Zea mays is maize and Bambusa vulgaris is bamboo.

(b) They have innumerable mouths and one exit.

Sponges (Porifera) take water in through many small pores (ostia) and expel it through one large opening, the osculum. They have no stomach, and their spicules are calcareous or siliceous, not chitin.

(d) Octopus

The octopus is the molluscan "devilfish". Loligo is the squid, Sepia the cuttlefish and Teredo the shipworm.

(b) Drone Adult

The honey bee life cycle has four stages: egg, larva, pupa and adult. "Drone adult" is a caste (a male adult bee), not a separate stage of the cycle.

(c) Lacrimal gland

The lacrimal gland is an exocrine gland: it secretes tears through ducts. The pituitary, adrenal and thyroid glands are ductless and release hormones directly into the blood.

(c) Parathyroid hormone (PTH)

PTH is secreted by the parathyroid glands, not the pituitary. The anterior pituitary secretes GH, FSH, LH, TSH, ACTH and prolactin.

(b) Right atrium

The superior and inferior vena cava bring deoxygenated blood from the upper and lower body into the right atrium, which passes it to the right ventricle.

(c) Bone marrow

Blood consists of plasma, red blood cells, white blood cells and platelets. Bone marrow is a tissue that produces blood cells; it is not a component of blood.

(c) Conduction of food

Epithelial tissue protects, secretes and absorbs (and also senses stimuli). Conduction of food is done by the digestive tract as an organ system, using muscular peristalsis, not a primary function of epithelium.

(b) Lamarck

Jean-Baptiste Lamarck proposed that characters acquired during an organism's lifetime through use and disuse are passed to offspring. Weismann later disproved this with his germ plasm theory.

(c) Communication and coordination of body functions

The nervous system receives stimuli, processes them and sends signals through neurons to coordinate responses of body organs.

(c) Theophrastus

Theophrastus, a student of Aristotle, wrote on the classification and description of plants and is called the Father of Botany. Aristotle is the Father of Biology and Linnaeus the Father of Taxonomy.

(d) None of them

A semi-autonomous organelle has its own DNA and ribosomes and can make some of its own proteins. These are mitochondria and chloroplasts. The Golgi complex, endoplasmic reticulum and ribosomes do not have their own DNA, so none of the options fits.

(c) Number of chromosomes remains same, amount of DNA becomes double

During the S phase of interphase DNA replicates, so the DNA content doubles. Sister chromatids stay joined at the centromere, so the chromosome number is unchanged.

(c) Unicellular eukaryotes, Protista

In Whittaker's five-kingdom system Protista contains unicellular eukaryotes such as Amoeba and Paramecium. Prokaryotes are placed in Monera.

(d) Pteridophyta

Ferns are seedless vascular plants with true roots, stems and leaves, so they belong to Pteridophyta.

(a) 10 Å

In B-DNA the double helix has a diameter of about 20 Å, so its radius is about 10 Å. One turn is 34 Å long, with 10 base pairs spaced 3.4 Å apart.

(b) trapping of solar radiation on earth surface

Greenhouse gases such as $\mathrm{CO_2}$, $\mathrm{CH_4}$ and water vapour trap the heat radiated by the earth, which keeps the atmosphere warm. Global warming is a result of an enhanced greenhouse effect, not its cause.

(d) Transpiration

Transpiration is the loss of water as vapour from the aerial parts of a plant, mainly through the stomata of leaves.

(a) Pisum sativum

A scientific name follows binomial nomenclature. The genus name starts with a capital letter, the species name is written entirely in lower case, and the whole name is italicised (or underlined when handwritten).

(b) Camel

A grassland ecosystem includes grasses, grasshoppers, rabbits and eagles. The camel is an animal of the desert ecosystem.

(b) Radial Symmetry

Coelenterates (Cnidaria) such as Hydra and jellyfish have a body that can be divided into equal halves by any plane passing through the central axis, which is radial symmetry.

(d) Malaria

Filariasis (elephantiasis) and ascariasis are caused by nematodes. Malaria is caused by the protozoan Plasmodium.

(b) Larva

Worker bees feed the growing larvae with royal jelly and bee bread (pollen and honey). Larvae are the feeding stage; eggs and pupae are not fed.

(d) Secretion of thyroxin and calcitonin

The thyroid gland secretes thyroxine, which regulates metabolism, and calcitonin, which lowers blood calcium. Prolactin and oxytocin come from the pituitary and insulin from the pancreas.

(b) Thyroid hormone

Iodine is a component of thyroxine ($T_4$) and triiodothyronine ($T_3$). Its deficiency causes goitre.

(a) Tricuspid valve

The valve between the right atrium and right ventricle has three flaps and is the tricuspid valve. The bicuspid (mitral) valve is on the left side, and semilunar valves guard the exits of the ventricles.

(c) Blood clotting

Platelets (thrombocytes) are cell fragments that gather at a wound and release clotting factors, forming a plug and starting the fibrin clot. Oxygen is carried by red cells and infection is fought by white cells.

(c) Muscle

Blood, bone and tendon are connective tissues, each with cells in an extracellular matrix. Muscle is a separate tissue type made of contractile fibres.

(a) Overproduction of individuals and limited resources

Populations produce more offspring than the environment can support, so individuals compete for limited food, space and mates. This competition is the struggle for existence, and it drives natural selection.

(c) Motor control, coordination, posture and balance

The cerebellum coordinates voluntary movement and maintains posture and equilibrium. Vision, hearing and breathing are handled by the occipital lobe, temporal lobe and medulla respectively.

(b) R. Hooke

Robert Hooke first observed cells in 1665 in a thin slice of cork under a microscope.

(a) Mitochondrion and Chloroplast

These two organelles contain their own DNA and ribosomes and can make some of their own proteins, but also depend on the nucleus, so they are semi-autonomous.

(b) Metacentric

In a metacentric chromosome the centromere lies at the middle, giving two equal arms.

(a) Primary consumers

Herbivores feed directly on producers (plants), so they occupy the first consumer level.

(a) cell elongation

Auxin promotes elongation of cells in shoots (and so growth of the stem), and is also involved in apical dominance and phototropism. Seed dormancy is broken by gibberellins and fruit ripening is caused by ethylene.

(c) anaemophily

Anaemophily is pollination by wind. Entomophily is by insects, ornithophily by birds and hydrophily by water.

(d) Plant anatomy

Anatomy deals with internal structure, whereas morphology deals with external form and physiology with functions.

(c) to prepare food by the process of photosynthesis.

Chloroplasts contain chlorophyll and convert light energy into chemical energy stored as carbohydrates.

(a) Glucose and fructose

Sucrose is a disaccharide formed from one glucose and one fructose joined by a glycosidic bond.

(d) Carnivorous as well as omnivorous

Secondary consumers feed on primary consumers (herbivores). They may be strict carnivores or omnivores that eat both plants and animals.

(a) Triploblastic, acoelomate, and bilaterally symmetrical

Flatworms have three germ layers, no body cavity (coelom) and bilateral symmetry.

(c) Nephridia

Annelids such as earthworms excrete through nephridia. Malpighian tubules occur in insects, flame cells in flatworms and green glands in crustaceans.

(a) Drones

Drones are fertile male honey bees whose role is to mate with the queen. Workers are sterile females.

(c) Pituitary gland

The pituitary secretes tropic hormones that regulate other endocrine glands, and is itself controlled by the hypothalamus.

(b) Gigantism

Excess growth hormone in childhood, before the bone growth plates close, causes abnormal height. In adults it causes acromegaly. Deficiency in childhood causes pituitary dwarfism.

(c) Left atrium

Pulmonary veins return oxygenated blood from the lungs to the left atrium, which passes it to the left ventricle.

(c) Hemoglobin

Hemoglobin contains iron (heme) that binds oxygen reversibly in red blood cells.

(c) Skeletal muscle

Skeletal muscle is striated and under voluntary control. Cardiac muscle is striated but involuntary, and smooth muscle is non-striated and involuntary.

(c) On the Origin of Species

Darwin published it in 1859, setting out evolution by natural selection.

(c) Cranial nerves

The central nervous system consists of the brain (including the brainstem) and the spinal cord. Cranial nerves belong to the peripheral nervous system.

(a) G. Mendel

Gregor Mendel proposed the law of independent assortment from his dihybrid cross experiments on pea plants.

(b) Chloroplast

Chloroplasts carry out photosynthesis and make food for the cell, so they are called the kitchen of the cell.

(d) Interphase

Interphase is called the resting phase, though the cell is actually metabolically active, growing and replicating its DNA (G1, S and G2) before division.

(b) Heterotrophs

Consumers cannot make their own food and depend on producers or other organisms for it, so they are heterotrophs.

(a) Fern

Ferns are pteridophytes and have xylem and phloem (vascular tissue). Algae, blue-green algae and Marchantia (a liverwort) lack vascular tissue.

(c) Chlorofluorocarbon

CFCs rise to the stratosphere, where UV light releases chlorine atoms that catalytically break down ozone ($\mathrm{O_3}$) into $\mathrm{O_2}$.

(a) bird

Ornithophily is pollination by birds, such as sunbirds. Pollination by insects is entomophily and by bats is chiropterophily.

(a) Xerophytes

Xerophytes are desert plants adapted to dry habitats. Algae, lotus and lily are typical pond ecosystem components.

(a) α-glucose

Glycogen is a branched polysaccharide of α-glucose units joined by α-1,4 and α-1,6 glycosidic bonds.

(d) mycota

Mushrooms are fungi (kingdom Fungi, also called Mycota). They are non-green, heterotrophic and have chitin in their cell walls.

(d) both B & C

Round worms (nematodes) have a pseudocoelom and a complete digestive tract with mouth and anus. Their body is unsegmented.

(d) Malpighian tubules

In insects and other arthropods, Malpighian tubules remove nitrogenous waste from the haemolymph and pass it into the gut.

(b) Apiculture

Apiculture is the rearing of honeybees for honey and wax. Sericulture is silkworm rearing, pisciculture is fish farming and horticulture is garden cultivation.

(c) Epinephrine

Epinephrine (adrenaline) from the adrenal medulla prepares the body for fight or flight by raising heart rate, blood pressure and blood glucose.

(b) Calcitonin

Calcitonin from the thyroid gland lowers blood calcium by inhibiting bone resorption. Parathyroid hormone does the opposite.

(b) Left ventricle

The left ventricle pumps blood at high pressure to the whole body through the aorta, so it has the thickest muscular wall. The right ventricle only pumps blood to the nearby lungs, and the atria receive blood and have thin walls.

(a) Erythrocytes

"Erythro" means red and "cyte" means cell. Monocytes and leukocytes are white blood cells.

(b) Storing energy as fat

Adipose tissue is a connective tissue made of fat-storing cells (adipocytes). It stores energy as fat and also insulates the body and cushions organs.

(b) better adapted

Natural selection favours individuals whose inherited traits suit their environment. These survive and reproduce more, passing those traits on.

(c) Cerebrum

The cerebrum is the largest part of the brain and is the seat of intelligence, memory, conscious thought and decision-making. The cerebellum controls balance, and the medulla controls involuntary actions such as breathing.

(b) Produces seeds in cones

Gymnosperms (e.g. pine) bear naked seeds, usually on cone scales, without flowers or fruits. They have vascular tissues.

(c) Movement of chromosomes

The centromere carries the kinetochore, where spindle fibres attach. This lets the chromatids or chromosomes move to the poles during anaphase.

(d) The apex of the food pyramid

The chain is plant → insect → snake → peacock. The peacock is the top (tertiary) consumer, at the apex.

(c) Selfing and noting that all progeny are tall

A pure (homozygous) tall plant $TT$ gives only tall offspring on selfing. A hybrid $Tt$ gives tall and dwarf in a $3:1$ ratio.

(b) Vivipary

Vivipary is germination of the seed while still inside the fruit on the parent plant, as in mangrove (Rhizophora).

(b) Angiosperms

In flowering plants one male gamete fuses with the egg (syngamy) and the other fuses with the two polar nuclei (triple fusion) to form the endosperm.

(d) Uracil

DNA contains adenine, guanine, cytosine and thymine. Uracil replaces thymine in RNA.

(a) Digestive centres

Lysosomes contain hydrolytic enzymes that digest worn-out organelles and engulfed material, so they are called "suicide bags".

(b) A cell plate begins to form at telophase, whereas in animals a cleavage furrow is initiated at that stage

Plant cells divide by a cell plate laid down from the centre outward. Animal cells divide by a furrow pinching inward. Sister chromatids are identical in both, and spindle attachment is the same in both. Higher plants lack centrioles.

(b) Interferon

Interferons are proteins released by virus-infected cells. They make neighbouring cells resistant to viral replication.

(b) Originate from pre-existing life

All living things arise from existing life (biogenesis). Not all need oxygen, and nutrition may be autotrophic or heterotrophic.

(c) Heparin

Heparin is a natural anticoagulant (made by mast cells and basophils) that stops blood clotting inside vessels. Fibrinogen, platelets and prothrombin promote clotting.

(b) Descent with modifications

Evolution is the gradual change of populations over generations, so that descendants differ from their ancestors.

(b) Commensalism

In commensalism one species benefits and the other is neither harmed nor helped, e.g. an orchid growing on a tree.

(b) Semicircular canals

The semicircular canals in the inner ear detect rotation and changes in head position, so they maintain balance when turning.

(a) Enzymes

Enzymes are biological catalysts, mostly proteins, that speed up metabolic reactions. Hormones regulate; they do not catalyse.

(d) Its length enables greater scope for food absorption

The small intestine is long, with villi and microvilli, to give a large surface area for absorbing digested food.

(c) Thinking

Sneezing, blinking and the knee jerk are involuntary, rapid reflex actions. Thinking is a voluntary higher function of the cerebrum.

(d) Fluorine

Fluoride strengthens tooth enamel and prevents dental caries. Too much causes fluorosis.

(d) Shark

A shark is a cartilaginous fish that breathes through gills. Porpoises, walruses and seals are mammals.