Biology: Model Question Sets and Predicted Questions

1. (b) — enzymes are globular proteins (a few catalytic RNAs exist but are not "most").

2. (b) — metaphase is the stage of alignment at the metaphase plate.

3. (c) — fungal walls are made of chitin; cellulose is the plant wall and peptidoglycan is bacterial.

4. (b) — the gametophyte is the conspicuous green plant, and the sporophyte depends on it.

5. (c) — energy is lost at every trophic level, so the energy pyramid is always upright; numbers and biomass can be inverted.

12. (b) — Lamarck, "use and disuse" and inheritance of acquired characters.

13. (b) — two atria and one ventricle.

14. (c) — nephridia (septal, pharyngeal and integumentary).

15. (b) — ethology; ethnology is the study of peoples.

16. (b) — decibel (dB).

17. (b) — same basic structure, different functions: homologous.

6. Mitosis versus meiosis.

7. Lichen. A lichen is a symbiotic association between an alga (or cyanobacterium) and a fungus: the alga makes food by photosynthesis and the fungus gives water, minerals and shelter. Importance: (i) they are indicators of air pollution, because they are very sensitive to sulphur dioxide and disappear from polluted air; (ii) they are pioneers of primary succession on bare rock, weathering it into soil; (iii) they yield dyes and indicators, such as litmus and orcein, and some are used as food and fodder (reindeer moss).

8. Economic importance of Fabaceae. (i) Pulses such as gram, pea, lentil, soybean and groundnut are rich sources of protein. (ii) The roots bear root nodules with Rhizobium, which fix atmospheric nitrogen and enrich the soil, so these plants are used in crop rotation. (iii) Timber and fuel are obtained from plants such as sissoo (Dalbergia sissoo). (iv) Others give fodder, dyes and medicine; for example indigo gives a dye and liquorice has medicinal use.

9. Eutrophication. Eutrophication is the enrichment of a water body with nutrients, especially nitrates and phosphates, leading to excessive growth of algae and aquatic plants. Causes: run-off of chemical fertiliser from farms, discharge of sewage and detergents. Effects: (i) an algal bloom covers the surface and blocks sunlight; (ii) when the algae die, bacteria decompose them and use up dissolved oxygen; (iii) fish and other animals die for lack of oxygen, and the water becomes foul and unfit to use.

18. Homologous organs have the same fundamental structure and origin but different functions, as in the human forelimb, whale flipper and bat wing; they show divergent evolution and common ancestry. Analogous organs have different structure and origin but the same function, as in the wing of an insect and the wing of a bird; they show convergent evolution. A homologous pair is evidence of common descent; an analogous pair is evidence of adaptation to similar conditions.

19. Lamarck's theory. Lamarck (1809) proposed that (i) organisms respond to the environment; (ii) organs that are used become better developed while organs that are not used weaken (use and disuse); (iii) these acquired characters are inherited by the offspring. Example: the long neck of the giraffe, which Lamarck explained by ancestors stretching to reach high leaves, the stretch being passed on. Criticism: acquired characters, such as a cut tail, are not inherited (Weismann cut the tails of mice for many generations and the offspring still had tails).

20. Excretion in the earthworm. The excretory organs are coiled tubes called nephridia, which are of three kinds: (i) septal nephridia on the septa, opening into the intestine; (ii) integumentary nephridia in the body wall, opening on the outside through pores; (iii) pharyngeal nephridia around the pharynx, opening into the buccal cavity. Each nephridium begins with a funnel (nephrostome) with cilia, collects waste from the coelomic fluid, and passes it along the tube, where useful substances and water are reabsorbed. The earthworm is ureotelic: the main waste is urea.

21. In-situ conservation protects species in their natural habitat, for example in Chitwan National Park and the Koshi Tappu Wildlife Reserve. Ex-situ conservation protects species outside their natural habitat, for example in the Central Zoo at Jawalakhel and the gharial breeding centre at Kasara in Chitwan.

10. Mitosis. Definition. Mitosis is the division of a somatic cell in which the nucleus divides into two nuclei with the same chromosome number as the parent (karyokinesis), usually followed by division of the cytoplasm (cytokinesis).

Stages. Diagram: one labelled sketch for each of the four stages, showing the spindle and the chromosomes. (i) Prophase — chromatin condenses into chromosomes, each of two chromatids joined at the centromere; the nucleolus and nuclear envelope disappear; the spindle begins to form. (ii) Metaphase — the chromosomes line up at the equator (metaphase plate) and the spindle fibres attach to the centromeres. (iii) Anaphase — the centromeres split and the sister chromatids are pulled to opposite poles. (iv) Telophase — the chromosomes reach the poles and uncoil; the nuclear envelope and nucleolus reappear; cytokinesis divides the cell (by cell plate in plants and by furrow in animals).

Significance. Mitosis gives growth and the replacement of worn cells, repair of wounds, and asexual reproduction, and it keeps the chromosome number constant in all body cells.

11. Solanaceae (the potato family). Vegetative characters: herbs, shrubs or small trees; leaves alternate, simple, without stipules; stems often with bicollateral vascular bundles; some have underground tubers (potato). Floral characters: flowers bisexual, actinomorphic, pentamerous and hypogynous; calyx of five sepals fused (gamosepalous, often persistent); corolla of five petals fused (gamopetalous); five stamens epipetalous (attached to the petals); gynoecium of two fused carpels (bicarpellary, syncarpous) with a superior ovary, axile placentation and a swollen placenta. The fruit is a berry or capsule.

Floral formula: ⊕ ⚥ K(5) C(5) A5 G(2) (⊕ actinomorphic, ⚥ bisexual, brackets show fused parts; the ovary is superior).

Economic importance. Food: potato (Solanum tuberosum), brinjal (Solanum melongena), tomato, chilli (Capsicum). Drugs: belladonna (Atropa) gives atropine; datura is medicinal and poisonous. Others: tobacco (Nicotiana), and ornamentals such as petunia.

22. Digestive system of the frog. The frog is carnivorous; its digestive system has the alimentary canal and digestive glands.

Diagram: a labelled sketch showing the mouth, buccal cavity, oesophagus, stomach, small intestine (duodenum, ileum), large intestine (rectum), cloaca, liver with gall bladder, and pancreas.

Alimentary canal. (i) The mouth opens into the buccal cavity, which has maxillary and vomerine teeth to hold prey and a bifid, sticky tongue, folded back and flicked out to catch insects. (ii) The cavity leads into the pharynx and a short oesophagus. (iii) The stomach is a J-shaped muscular bag with gastric glands that secrete HCl and pepsin; food becomes a semi-fluid chyme. (iv) The small intestine has the duodenum, where bile and pancreatic juice enter, and the coiled ileum, where digestion is completed and food is absorbed. (v) The large intestine (rectum) stores undigested matter, which leaves through the cloaca and the cloacal aperture.

Digestive glands. The liver secretes bile, which is stored in the gall bladder and emulsifies fats. The pancreas secretes pancreatic juice with enzymes (amylase, trypsin, lipase) that act in the duodenum.

23. Evidences of organic evolution.

Comparative anatomy. (i) Homologous organs such as the forelimbs of a human, a whale and a bat have the same plan but different uses and show common ancestry. (ii) Analogous organs such as the wings of insects and of birds show adaptation to the same function. (iii) Vestigial organs such as the vermiform appendix and the ear muscles are reduced remains of organs that were functional in ancestors.

Embryology. The embryos of fish, frog, chicken and human look alike in early stages and diverge later, showing common ancestry. Haeckel's biogenetic law says that ontogeny repeats phylogeny, and the tadpole of the frog with gills and a tail recalls its fish-like ancestors. (Haeckel's law is now held to be only partly true.)

Palaeontology. Fossils are remains or impressions of ancient organisms in rocks. The order of fossils in the layers shows the sequence of life from simple to complex. Connecting links such as Archaeopteryx, which has feathers like a bird and teeth and a tail like a reptile, link reptiles to birds. The fossil series of the horse shows a gradual change in size, toes and teeth.

1. (a) — Schleiden (plants) and Schwann (animals), 1838–39; Hooke only named "cells".

2. (b) — Emil Fischer (1894); Koshland proposed the induced-fit model.

3. (c) — Monera contains bacteria and cyanobacteria.

4. (b) — "gymnosperm" means naked seed; there is no ovary and no fruit.

5. (b) — Rhododendron arboreum (lali gurans).

12. (b) — amino acids formed from methane, ammonia, hydrogen and water vapour under electric sparks.

13. (b) — metamerism, also called metameric segmentation.

14. (b) — Cnidaria, with stinging cells (cnidoblasts).

15. (c) — carbon dioxide is the main greenhouse gas from human activity.

16. (b) — Pavlov trained dogs to salivate at the sound of a bell.

17. (b) — the tadpole has external gills at first, then internal gills, and lungs only after metamorphosis.

6. Functions of the Golgi apparatus. (i) It modifies and packages proteins and lipids received from the endoplasmic reticulum. (ii) It secretes substances out of the cell in vesicles (such as enzymes and mucus). (iii) It forms lysosomes. (iv) It adds sugar groups to make glycoproteins and glycolipids, and in plant cells it helps in forming the cell wall and cell plate; in sperm it forms the acrosome.

7. Characters of Bryophyta. (i) They are non-vascular plants with no xylem or phloem. (ii) The plant body is a gametophyte and is dominant; it is thalloid or leafy and is fixed by rhizoids. (iii) The sporophyte is dependent on the gametophyte for water and food. (iv) Water is needed for fertilisation, because the male gametes swim; for this reason bryophytes are called the "amphibians of the plant kingdom". (v) Reproduction is vegetative (by gemmae) and sexual.

8. Ecological adaptation. It is a structural, functional or behavioural feature that helps an organism survive in a particular habitat. Hydrophytes (water plants): (i) roots are reduced or absent; (ii) tissue has large air spaces, aerenchyma, for buoyancy and gas exchange; (iii) floating leaves bear stomata only on the upper surface. Xerophytes (desert plants): (i) a thick cuticle and sunken stomata reduce water loss; (ii) leaves are reduced to spines, and stems are fleshy and photosynthetic; (iii) deep roots reach water. (Any two of each are enough.)

9. DNA versus RNA.

18. Vestigial organs are reduced, non-functional (or little-used) remains of organs that were fully functional in the ancestors. Examples in humans: (i) the vermiform appendix; (ii) the ear muscles (auricular muscles); (iii) the coccyx (tail bone); (iv) the wisdom teeth; (v) the nictitating membrane at the inner corner of the eye. They are evidence of evolution.

19. Phylum Arthropoda. (i) The body is segmented and divided into head, thorax and abdomen (or fused regions). (ii) There are jointed appendages, which gives the phylum its name. (iii) The body is covered by a chitinous exoskeleton, which is moulted (ecdysis). (iv) The circulatory system is open, with a body cavity called a haemocoel, and a dorsal heart. (v) There are paired compound eyes, and respiration is by gills, book lungs or tracheae. Examples: prawn, butterfly, spider, cockroach.

20. Amoeba: (i) the shape is irregular and changing; (ii) it moves and feeds by pseudopodia; (iii) it has one nucleus; (iv) it multiplies by binary fission only. Paramecium: (i) the shape is fixed, slipper-like, because of the pellicle; (ii) it moves by cilia and feeds through an oral groove; (iii) it has two nuclei, a macronucleus and a micronucleus; (iv) it multiplies by binary fission and also shows conjugation.

21. Innate versus learned behaviour.

10. Meiosis I. Meiosis is the division of a reproductive cell in which the chromosome number is halved. Meiosis I is the reductional division.

Diagram: labelled sketches of each stage showing paired chromosomes, the spindle and the nuclear envelope.

(i) Prophase I is long and has five sub-stages: leptotene (chromosomes become thread-like), zygotene (homologous chromosomes pair up, called synapsis, to form bivalents), pachytene (the pairs shorten, and crossing over occurs between non-sister chromatids), diplotene (the homologues begin to separate and are held at the chiasmata) and diakinesis (the chromosomes are fully condensed, and the nucleolus and nuclear envelope disappear). (ii) Metaphase I — the bivalents line up at the equator, with the spindle fibres attached to the centromeres of each homologue. (iii) Anaphase I — the homologous chromosomes separate and move to opposite poles; the centromeres do not divide. (iv) Telophase I — two haploid nuclei form, and the cell divides into two. Meiosis II then follows and divides the chromatids as in mitosis, giving four haploid cells.

Significance. (i) It halves the chromosome number in gametes, so fertilisation restores the diploid number. (ii) Crossing over and random separation produce genetic variation. (iii) Variation is the raw material of evolution.

11. Brassicaceae (the mustard family, formerly Cruciferae). Vegetative characters: herbs, rarely shrubs; leaves alternate, simple, without stipules, often with a pungent smell and taste. Floral characters: the flowers are bisexual, actinomorphic and hypogynous; the calyx has four sepals in two whorls (2+2), free; the corolla has four petals arranged like a cross (cruciform); there are six stamens in two whorls, of which the outer two are short and the inner four long (tetradynamous); the gynoecium has two fused carpels (bicarpellary, syncarpous) with a superior ovary, parietal placentation, and a false partition called the replum. The fruit is a siliqua or silicula.

Floral formula: ⊕ ⚥ K2+2 C4 A2+4 G(2) (superior ovary).

Economic importance. Vegetables: cabbage, cauliflower, radish, turnip and broccoli. Oil: mustard and rapeseed oil are obtained from the seeds of Brassica. Spice: mustard seeds. Ornamentals: candytuft and wallflower.

22. Respiratory system of the frog. The frog breathes in three ways: through the skin (cutaneous), through the lining of the mouth (buccopharyngeal) and through the lungs (pulmonary). The skin is thin, moist and rich in blood capillaries, and it is the main route during hibernation and when in water.

Pulmonary respiratory organs. The system has external nostrils, the nasal passage, the buccal cavity, the glottis, the laryngo-tracheal chamber and a pair of lungs. The lungs are two thin-walled, elastic sacs with many folds, lined with capillaries, and they lie in the upper part of the body cavity.

Mechanism of breathing. (i) Inspiration: the floor of the buccal cavity is lowered, the nostrils are open and the glottis is closed, so air enters the buccal cavity. Then the nostrils close, the glottis opens and the floor of the cavity is raised, forcing air into the lungs. (ii) Gas exchange takes place in the lungs between air and blood. (iii) Expiration: the body wall muscles contract and the lungs recoil, so air is pushed out through the glottis and the nostrils.

23. Darwin's theory of natural selection. Charles Darwin put forward the theory in On the Origin of Species (1859), after his voyage on the Beagle. Alfred Russel Wallace reached the same idea independently.

Postulates. (i) Overproduction: organisms produce many more offspring than can survive. (ii) Struggle for existence: because resources are limited, the offspring compete for food, space and mates, and face enemies and disease. (iii) Variation: the members of a species differ from each other, and some variations are inherited. (iv) Natural selection or survival of the fittest: those with favourable variations survive and reproduce, and the others die. (v) Origin of new species: over many generations the favourable variations accumulate, and a new species arises.

Example: industrial melanism in the peppered moth (Biston betularia). Before industrialisation in England most moths were light and matched the light, lichen-covered tree trunks, so birds ate the dark ones. As soot darkened the trunks, dark moths were camouflaged and light ones were eaten, so the dark form became common. Natural selection thus acted on a variation that already existed. A second example is antibiotic resistance in bacteria.

Limitation. Darwin could not explain how variations arise or are inherited, which was later explained by genetics and mutation.