Q 1. Who first described meiosis?
. Strasburger,
Q 2. What is a genome?
It is a full set of DNA instructions or a single set of chromosomes in a cell.
Q 3. What is meant by the non-disjunction of chromosomes?
Non-disjunction means failure in the separation of homologous chromosomes during anaphase.
Q 4. Why is mitosis an equational division?
Mitosis is an equational division because the daughter cells get the same number of chromosomes from the parent.
Q 5. What is crossing over?
The exchange of segments of chromatids of homologous chromosomes during meiosis is called crossing over.
Q 6. Why is meiosis a reductional division?
Meiosis is a reductional division because it reduces the number of chromosomes from diploid number to haploid number in the daughter cells.
Q 7. What are the two successive divisions in meiosis?
The first division is reductional followed by the second equational di¬vision.
Q 8. Name the two phases of the cell cycle of a somatic cell.
- Interphase and
- M-phase or mitotic phase
Q 9. During which part of interphase active synthesis of RNA and proteins take place.
G. phase.
Q 10. What amount of DNA is present in the cell during the G2 phase?
Double the amount of DNA present in the original diploid cell.
Q 11. What is a kinetochore?
A part of the chromosome for the attachment of chromosomal fibers.
Q 12. Define Eumitosis.
Chromosomes are attached to the spindle by their centromere and this type of mitosis is called Eumitosis.
Q 13. Define cell cycles.
The cell cycle is the sequence of events that occur between the formation of a cell and its division into daughter cells.
Q 14. What do you understand by homologous chromosomes?
Homologous chromosomes are pairs of chromosomes that have similar characteristics. They show pairing during meiosis. One chromosome in each pair is inherited from the father and the other one from the mother.
Q 15. Why is mitosis an equational division?
Mitosis is an equational division because the daughter cells have the same number of chromosomes and an equal amount of cytoplasm..
Q 16. Who gave the term mitosis?
W. Flemming.
Q 17. How many mitotic divisions will be required to produce 128 daughter cells from a single cell?
127.
Q 18. What is the Gj phase of the interphase?
It is the first period of growth of the neatly formed undivided cells, during which the cell synthesizes a lot of RNA and proteins.
Q 19. Why is meiosis necessary in sexually reproducing organisms?
Meiosis is necessary for sexually reproducing organisms because
- It maintains the number of chromosomes constant in generation as meiosis is reductional division.
- It causes variations among the progeny because crossing over takes place during meiosis. This variation is important for evolution.
Q 20. What is the importance of mitosis
Mitosis is important because
- It maintains genetic stability through generations.
- It helps in the growth of multicellular organisms.
- Many plants and animals multiply by mitosis i.e., asexual repro-duction to regenerate the whole organism.
- It helps to regenerate lost parts of an animal’s body.
- It helps in the regeneration of new cells in place of dead and worn-out cells.
Q 21. What are homologous chromosomes? What happens to homologs during meiosis?
Each diploid nucleus has pairs of similar chromosomes called homologous chromosomes. The two homologous chromosomes each derived from one parent during sexual reproduction come together and form pairs during the zygonema of meiosis I. Individuals of a pair are similar in length and in the position of their centromere.
Q 22. What is the significance of meiosis?
Significance of meiosis:
- Sexual reproduction: Maintains a number of chromosomes constant. Characteristic of a species from generation to generation.
- Genetic variation: Through crossing over, it produces variations of genetic characters of the progeny essential for evolution.
Q 23. What do you mean by cell reproduction?
Cell reproduction: Reproduction is an essential phenomenon in the continuity of life. New cells arise by the division of the pre-existing cells. It was proposed by Rudolf Virchow.
Reproduction is of two types:
- sexual and
- asexual reproduction.
The growth and development of the living being are dependent on the division of cells. The single-celled zygotes by means of cell division develop into an adult having a large number of cells.
Q 24. What is P-oxidation?
Fats are broken down into glycerol and fatty acids during digestion. Glycerol enters the glycolytic pathway at the triose phosphate stage. Fatty acids undergo β oxidation by which two-carbon fragments of acetyl A are split off at a time from the fatty acid chain so that the long fatty acid molecule is shortened by two carbon-carbon atoms at a time. This ultimately results in incomplete oxidation of fatty acids.
Q 25. Distinguish between the Anaphase of mitosis and the Anaphase of meiosis I.
| Anaphase of mitosis | Anaphase of Meiosis I |
| (i) Centromeres divide into two | (i) Centromeres do not separate the chromosomes. |
| (ii) Chromatids separate and move towards the opposite direction | (ii) Half number of chromosomes move towards opposite poles. |
| (iii) Separated chromatids are identical. | (iii) Separated chromosomes are homologous. |
Q 26. Distinguish between combustion and respiration
Ans.
| Combustion | Respiration |
| (i) It is a non-living process. | (i) It is a biological process, taking place in cells of living organisms. |
| (ii) It oxidizes the substrate releasing the entire energy at once. | (ii) It brings about oxidation of organic compounds releasing energy stepwise. |
| (iii) The energy released is in the form of heat and sometimes partly as light. | (iii) The chemical energy is either made available to the cell or stored in it as ATR |
| (iv) Heat is generated in large amounts. | (iv) The heat is generated in small amounts and does not harm the cell. |
Q 27. Distinguish between mitosis and meiosis.
| Mitosis | Meiosis |
| 1. It takes place in somatic or vegetative cells. | 1. It takes place in gametic or reproductive cells. |
| 2. Completes in one sequence or phase. | 2. Completes in two sequences or phases. |
| 3. Form two daughter cells that are diploid. | 3. Form four haploid daughter cells. |
| 4. Prophase is short and completes in one step. | 4. Prophase I is long and complicated. It completes in five steps. |
| 5. Crossing oyer does not take place. | 5. Crossing over takes place during prophase. |
| 6. Daughter cells are identical to each other and the parent cells. | 6. Daughter cells are not identical to each other and the parent cells show variations. |
Q 28. Describe the changes that take place during the prophase and metaphase of mitosis.
Following changes take place during prophase
- Chromosomes become short and thick and sister chromatids are held at the centromere.
- Nucleus and nuclear envelope disappear.
- In animal cells, centrioles move to opposite poles.
- Chromosomes begin to move towards the equatorial plane.
Following changes take place in metaphase:
- Chromosomes lie on the equatorial plate.
- Chromatids become attached by spindle fibers.
- Maximum condensation of chromosomes takes place.
Q 29. Explain the main steps in aerobic glycolysis.
Ans. Glycolysis is the breakdown of glucose to pyruvic acid, which includes the following:
(a) Phosphorylation: Transfer of phosphate from ATP to glucose to form glucose – 6 phosphate. One molecule of ATP is consumed enzyme, hexokinase is present.
(b) Isomerisation: There is internal molecular rearrangement to form fructose 6 phosphates. The enzyme is hexose phosphate isomerase.
(c) Second phosphorylation: The fructose – 6-phosphate undergoes phosphorylation to form fructose 1,6 diphosphate. One molecule of ATP is consumed. The enzyme is phosphofructokinase.
(d) Triose phosphates are 3-phosphoglyceraldehyde (PGAL) and dihydroxyacetone phosphate (DHAP). The enzyme phosphorize isomerase maintains the two isomers in equilibrium.
(e) Phosphorylation and oxidative dehydrogenation: PGAL under¬goes simultaneous phosphorylation and oxidative dehydrogenation to form 1,3 diphosphoglyceric acid.
(f) ATP generation: 1,3 diphosphoglyceric acid transfers its phosphate with a high energy bond to ADP to form ATP and 3-phosphoric acid. One molecule of ATP is produced from one triose molecule.
One enzyme is phosphoglyceric kinase Glucose
Q 30. How cytokinesis is different in an animal and a plant cell?
Cytokinesis in plant and animal cells: The separation of daughter nuclei and cytokinesis or cell cleavage maybe two different processes. The first visible changes consist of an appearance of dense material around the microtubules at the equator of the spindle at either mid or late phase then although spindle the fibre tends to disorganize and disappear during telophase, they usually persist and may even increase in number at the equator, frequently intermingled with a row of vesicles and the dense material.
The entire structure is called the midbody. Simultaneously there is a depression on the cell surface a kind of constriction that deepens gradually until reaching the midbody with the completion of the furrowing, the separation of cells is concluded.
The phragmoplast begins to form in the mid anaphase of plant cells. Under the electron microscope, it is possible to observe that the vesicles are of dense material applied together to their surface. The vesicles are derived from Golgi complexes which are found in the regions adjacent to phrag¬moplast which migrate to the equatorial region to be clustered around the microtubules.
Although phragmoplast is initially found as a ring on the periphery of the cell, with time it grows centripetally by the addition of microtubules and partition until it extends across the entire equatorial plane. The vesicles increase in size and just until the two cells are separated by a fairly continuous plasma membrane.
All this time the phragmoplast has been transformed into, cell plate. Thin cytoplasmic connection is plasmoids- data transverse the cell plate and remain in place for communication between the adjacent daughter cells.
The formation of the cell plate also leads to the synthesis of the cell wall. The Golgi-vesicles in phragmoplast is already filled with secretory material consisting mainly of the pectin. The fusion of vesicles results in the combining of the pectin in the extracellular space between the two daughter cells thereby forming the main body of the periphery cell wall.
Q 31. Draw an ecological pyramid, depicting the trophic levels.
Q 32. Write the harmful effects of using plastic bags on the environment. Suggest alternatives to plastic bags.
Harmful effects of plastic bags
- They clog the drainage system.
- They choke the alimentary canal of cattle when they get eaten by them.
- On burning they release toxic gases.
- They are non-biodegradable and do not decompose easily.
Alternative to plastic bags:
- Use of jute bags or paper bags.
- Reusable cloth bags.
Q 33. What are the advantages of cloth bags over plastic bags during shopping?
Cloth bags are better than the plastic bags because they:
- can be used to carry many things
- can be reused
- are made of biodegradable materials
- do not pollute the environment.
Q 34. Differentiate between biodegradable and non-biodegradable substances with the help of one example each. List two changes in habit that people must adapt to dispose non-biodegradable waste for saving the environment.
1. Biodegradable substances: Substances that can be slowly destroyed and broken down into very small parts by natural processes by bacteria, fungi, etc. For example, organics wastes like vegetables and fruit peels.
2. Non-biodegradable substances: Substances that cannot be broken down or decomposed into the soil by natural agents are called as non-biodegradable. For example, plastic. Habits to dispose non-biodegradable waste are:
- Segregating and treating the non-biodegradable waste before putting in dustbins.
- Recycle the plastics or glass present in non-biodegradable wastes.
- Motivate people to use paper or jute bags instead of plastic bags.
Q 35. How is ozone formed in the higher level of the atmosphere? “Damage to ozone layer is a cause of concern”. Justify this statement.
Ozone is formed due to action of UV rays on oxygen molecules to form free oxygen atom which subsequently combines with another molecule of oxygen to form ozone. The reaction is:
O + O2 → O3 (Ozone)
Ozone depletion is a cause of concern because it protects us from the harmful ultraviolet radiations of the Sun by absorbing them. The UV rays can cause skin cancer, ageing, cataract, etc. to human beings if they are not absorbed by ozone due to ozone depletion.
Q 36. Explain phenomenon of “biological magnification”. How does it affect organisms belonging to different trophic levels particularly the tertiary consumers?
The levels of harmful toxicants/pesticides like DDT gets increased at successive trophic levels as they are neither metabolised nor excreted by the organism. They get accumulated in organism’s body with their higher concentrations at higher trophic levels. This is called as biological magnification.
Since, the tertiary consumers are at the top of the food chain, so a higher amount of these toxicants is present in them compared to the lower trophic levels.
Q 37. Suggest any four activities in daily life which are eco-friendly.
The eco-friendly activities in life are
- Planting of trees.
- Segregating biodegradable and non-biodegradable wastes.
- Using cloth bags, jute bags or paper bags instead of plastic bags.
- Creating awareness on environment protection through initiatives and campaigns.
- Using of manures and organic agricultural methods.
- Using less of chemical fertilizers and pesticides.
- Controlling pollution by using fuels like CNG.
Q 38. Make food chains in (i) forest (ii) grassland (iii) pond. How does food chain differ from a food web?
Food chains in:
(i) Forest: Plants → Deer → Lion
(ii) Grassland: Plants → Grasshopper → Frog → Snake → Eagle
(iii) Pond: Aquatic plants → Scorpion Fish → Flamingo
Food Chain: It is a series of organisms feeding on one another.
Food Web: It is a network of food chains consisting of a number of interlinked food chains.
Q 39. Indicate the flow of energy in an ecosystem. Why is it unidirectional?
The flow of energy generally is
Sun → Producer → Herbivore → Carnivore
The flow of energy is unidirectional because it goes progressively from one trophic level (lower) to another trophic level (higher) and does not revert back.
It is impossible for energy to flow in the reverse direction as the available energy decreases in the higher trophic levels.
Q 40. Name the wastes which are generated in your house daily. What measures would you take for their disposal?
The wastes generated in our house daily are:
- Kitchen wastes
- Paper wastes like newspapers, bags, envelopes
- Plastic bags
- Vegetable/fruit peels/rinds
The measures which can be taken for their disposal are:
- Segregate the wastes as biodegradable, non-biodegradable and hazardous ones.
- Dispose of the plastic bags and bottles in a proper way.
- Vegetable/fruit peels can be used to make compost.
- Paper wastes can be used for recycling.
- Prepare a vermicompost pit for the organic wastes from the kitchen.
Q 41. Explain some harmful effects of agricultural practices on the environment.
- Change in the chemistry of soil and killing of useful microbes due to excessive use of fertilisers.
- Biological magnification occurs due to excessive use of chemical pesticides.
- Water table gets lowered due to the excess use of ground water.
- Soil fertility is lost due to extensive cropping.
- The natural ecosystems is harmed due to ploughing during agriculture.
Q 42. “Energy flow in a food chain is unidirectional”. Justify this statement. Explain how the pesticides enter a food chain and subsequently get into our body.
Ans. The flow of energy in an ecosystem occurs from a lower trophic level to the next trophic level i.e., from producers to consumers. It follows the ten percent law and thus cannot return back to producers from consumers. Hence, the flow of energy in a food chain is unidirectional.
The pesticides like DDT enter the food chain after getting absorbed by plants from the soil. Once they enter the food chain, they are neither metabolized nor excreted from the body of the organism. Its concentration increases in the successive trophic level of the food chain.
Q 43. Rakshit observed a gardener collecting dry leaves from a garden and burning them. He went to the gardener and advised him to utilise the dry leaves for making manure instead of burning.
(a) Name the two process which can be used to make manures from the dry leaves.
(b) Why did Rakshit advise the gardener not to burn leaves?
(c) What are the values shown by Rakshit?
(d) Why are organic manure better than chemical fertilisers?
(a) Composting and vermicomposting
(b) Burning of leaves emits smoke and harmful gases which pollute the environment.
(c) Environment friendly, concern for life, awareness, scientific attitude, logical thinking, etc.
(d) Organic manures are better than chemical fertilisers as excess use of chemical fertilisers leads to (i) loss in soil fertility (ii) increase in soil salinity.
Q 44. The students of a school formed an Environment Club and started Campaign to Recycle waste, No cracker campaign and No-plastic campaign.
(а) What are the harmful effects of plastic waste?
(b) What are the alternatives to use of plastic bags?
(c) What are the values exhibited by the students of the school?
(d) Why is it necessary to recycle wastes?
(a) The excess use of plastics causes the following problems:
- It causes environmental pollution.
- Plastic bags are non-biodegradable and can cause problems in the digestive system of animals if they eat these plastic bags.
(b) Alternatives are the use of Jute bags or paper bags.
(c) Values are: Eco-friendliness, Concern for life, Responsible, Creative thinking.
(d) To reduce the amount of garbage generated.
Q 45. (a) How can we help in reducing the problem of waste disposal? Suggest any three methods.
(b) Distinguish between biodegradable and nonbiodegradable wastes.
Ans. (a) The three methods of waste disposal are:
(i) Recycling: solid, wastes like paper, plastics, metals can be sent to processing factories where they are remoulded or reprocessed to new materials.
(ii) Production of compost: Biodegradable wastes like fruit and vegetable peels, plant products, left over food, grass clippings, human and animal waste can be converted into compost by burying this waste into ground and can be used as manure.
(iii) Incineration: Burning dawn many household waste, chemical waste and biological waste into ash is known as incineration. A large amount of waste can be easily converted into ash which can be disposed off in landfill.
(b)
| Biodegradable wastes | Non-biodegradable wastes |
| (i) These wastes can be broken-down into non-poisonous substances in nature by the action of microorganisms. |
(i) These wastes cannot be broken down into non-isonous substances by microorganisms. |
| (ii) They get recycled thus, do not need any dumping sites. | (ii) They cannot be recycled thus, require dumping sites. |
| Biodegradable wastes | Non-biodegradable wastes |
| (i) These wastes can be broken-down into non-poisonous substances in nature by the action of microorganisms. |
(i) These wastes cannot be broken down into non-isonous substances by microorganisms. |
| (ii) They get recycled thus, do not need any dumping sites. | (ii) They cannot be recycled thus, require dumping sites. |
Q 46. (a) What is biodiversity? What will happen if biodiversity of an area is notpreserved? Mention one effect of it.
(b) With the help of an example explain that a garden is an ecosystem.
(c) Why only 10% energy is transferred to the next trophic level?
(a) Biodiversity is the existence of a wide variety of species of plants, animals and microorganisms in a natural habitat within a particular environment or existence of genetic variation within a species. Biodiversity of an area is the number of species or range of different life forms found there. Forests are ‘biodiversity hotspots’. Every living
being is dependent on another living being. It is a chain. If biodiversity is not maintained, the links of the chain go missing. If one organism goes missing, this will affect all the living beings who are dependent on it.
(b) A garden comprises of different kind of flora and fauna such as grasses, flowering and nonflowering plants, trees, frogs, insects, birds, etc. All these living organisms depend and interact with each other and their growth, reproduction and other vital biological activities depend upon the abiotic component comprising of physical factors like emperature, rainfall, wind, soil and minerals. Therefore, we can say that a garden is an ecosystem
(c) Only 10% energy is transferred to the next trophic level because other 90 per cent is used for things like respiration, digestion, running away from predators.