Question 1
Differentiate between zoospore and zygote? Answer
Zoospore
Zygote
It is the structure associated with asexual reproduction.
It is the structure formed as a result of fertilisation during sexual reproduction.
It germinates immediately, as it is formed during favourable conditions.
In algae and fungi, it undergoes a period of dormancy, as it is formed at the end of favourable season.
It is motile and uses flagella for movement.
It is non-motile.
It is generally thin walled.
It becomes thick walled in fungi and algae in order to resist damage and dessication.
Question 2
Under unfavourable conditions, Amoeba shows encystations. What does it mean? Answer
Under unfavourable conditions, Amoeba withdraws its pseudopodia and develops a three-layered thick wall around it, this process is known as encystations. Question 3
Name an algae reproduce through zoospores?
Answer
Chlamydomonas. Question 4 All papaya plants bear flowers, but fruits are seen only in some. Explain? Answer
Papaya is dioecious, the plant which produce only male flowers, do not bear fruits, while the plants which produce female flowers, bear fruits. Question 5
Both tapeworm and earthworm are hermaphrodites. How they are differ from each other with reference to fertilisation? Answer
Earthworm shows cross fertilisation where as tapeworm shows self fertilisation.
Question 6
Name the phenomenon and one bird where the female gamete directly develops into a new organism? Answer
Parthenogenesis. Turkey bird. Question 7 Name the common phenomenon with reference to reproduction in rotifers, honey bee?
Answer
Parthenogenesis. Question 8 In the whiptail lizard, only females are born generation after generation. There are no male. How is this possible? Answer
They show parthenogenesis, the phenomenon in which the female gamete undergoes development without fertilisation into adult. Question 9 Mention the site where syngamy occurs in amphibians and reptiles, respectively? Answer
In amphibians, it occurs in the medium of water i.e. external fertilisation.
In reptiles, it occurs inside the body of the female animals, i.e. inter fertilisation.
Question 10 Name the types of life-cyle in which zygote undergoes mitosis? Answer
Haplo-diplontic life-cycle and diplontic life-cycle. Question 11 Unicellular organisms are immortal, whereas multicellular organisms are not. Justify? Answer
Since single celled organisms are reproduce by cell division, there is no natural death for them, they are considered immortal. In multicellular organisms, reproduction occurs in specialised organs involving specialised cells, their body as a whole dies due to ageing and senescence. Question 12 Why it is difficult to get rid of ‘water hyacinth’ from water body? Name on abiotic and one biotic component of the ecosystem that gets affected by its spread in the water body? Answer
It is difficult to get rid of them because they propagate vegetatively at a rate faster than we could remove them.
It drains oxygen from the water.
It leads to fish mortality i.e. death of fishes.
Question 13 Banana crop is cultivated by farmers without sowing of seeds. Explain how the plant is propagated? Answer
In banana, the modified underground stem is called rhizome.
Small plantlets arise from the buds present in the nodes and tips of branches, when come in contact with the damp soil or water. These plantlets are then separated and grown as new individual plants.
Question 14 In general, the male gametes are motile, while the female gametes are stationary. Mention two types of exception to this, with an example for each? Answer
Both male and female gametes are non-motile, for example certain algae and few fungi.
In seed plants, the male gametes are non-motile and are carried in the pollen tube to the egg.
Question 15 Write two adaptations in animals exhibiting external fertilisation? Answer
There is great synchrony between the two sexes, i.e. they release the mature gametes simultaneously. They release a large number of gametes in the surrounding medium (water) to enhance the chances of syngamy. Question 16 Describe the process of sporulation seen in Amoeba? Answer
Sporulation is the process in which the products of multiple fission become individually surrounded by a cyst wall before being released from the parent, each of them is a spore.
The sporulation remain dormant during unfavourable conditions and germinate when conditions become favourable. Advantages-
Being thick walled, it helps to tide over the unfavourable conditions.
It is also mean of dispersal to different location.
Question 17 Although potato tuber is an underground part, t is considered as stem, why? Answer
The tuber has nodes and internodes which are a part of a stem.
Leafy shoots appear from the nodes.
Question 18 Why do we say that there is no natural death in single celled organisms? Answer
Single celled organisms reproduce by cell division (into two new individuals), there is no natural death for them. Question 19 Algae and fungi shift to sexual method of reproduction just before the onset of adverse conditions. Find out how sexual reproduction enables these organisms to survive during unfavourable conditions? Why is sexual reproduction favoured under such conditions? Answer
In algae and fungi, the zygote formed as a result of sexual reproduction, develops a thick wall, which protects the zygote from desiccation and mechanical injuries; hence the zygote is able to remain the dormant during the unfavourable condition and germinate at the return of favourable conditions.
Since sexual reproduction brings in variation, at least some variants will be able to survive, in case of an adverse change in the environmental conditions.
Because of the survival advantages, sexual reproduction is favoured under such conditions. Question 20 Can you identify cases where self-fertilisation is observed? Answer
Plants with bisexual flowers (like Pea, Commelina, Viola etc) that show autogamy.
Animals like tapeworm.
Question 21 Why do intermodal segments of sugarcane fails to propagate vegetatively, even when they are in contact with damp soil? Answer
The plantlets arise from the buds present on the nodes, only when the nodes comes in contact with the damp soil, will they produce roots and shoots and not from intermodal segments.
