Question

14:

a. Describe three factors that are most important for primary productivity on land. Are those same three factors also important for primary productivity in aquatic ecosystems? What is the most important limitation on terrestrial primary productivity and is it the same in aquatic ecosystems?

b. Pick two different examples of how organisms carry out sexual reproduction and describe their similarities and differences. You will be evaluated more positively if the mechanisms are quite different.

Answer 1

Describe three factors that are most important for primary productivity on land. Are those same three factors also important for primary productivity in aquatic ecosystems?

Ans - 1. Light

2. Water availability

3. Carbon dioxide

All these factors are necessary for increasing the productivity of primary producers that are autotrophic and make their food by these three factors. Sunlight gives energy for the process of photosynthesis , water and carbon dioxide are used as substrates in this process.

Among these only light is essential in the aquatic ecosystem.

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Lack of water is the major limiting factor of primary productivity. As we can related to the productivity of rain forests and any of the deserts. Less water leads to lesser primary productivity. And this is not a limiting factors in case of primary productivity in aquatic ecosystem.

Pick two different examples of how organisms carry out sexual reproduction and describe their similarities and differences.

1. Sexual reproduction in flowering plants

In which stamens is the male spore bearing organ which has pollen grains and pistil is the female reproductive organ which contains the ovule in its ovary. Now the pollen grains that fertillise the flower comes from the same plant or different plant of the same species. Stamen has motile anthers which contains pollen grains that on reaching stigma which is sticky surface on pistil geminates by forming a pollen tube and then release the pollen grains near the ovule and fertillizes it.

2. Sexual reproduction in humans/ animals

Male has sperms which are motile and female has an egg which is non- motile. Male approaches female and copulation takes place during which male reproductuve organ is used to ejaculate sperm in female reproductive organ from where the sperm flows and reaches the egg present in the fallopian tube and fertillizes it.

Difference in both the examples: Transportation of male motile gametes. In flowering plants anthers that have pollen grains which are the male gametes can be traported by wind, air, water but in case of human and animals only ejaculation or artificial insemination can do that.

Similarity: Motile male sperms and non motile female egg

One more example can be discussed like in fishes and amphibians - both parents release there gametes in the water in huge number and the egg finds its species specific male gamete and fertilizes outside the female body and developes on its own.

Similarity is different sex gametes come together and fuse making a zygote.

Difference- external fertillisation and development of the zygote. Flowering plants, animals and humans have internal fertillisation and development.