Organisms and Populations — BIOLOGY STD 12 Science — Question

Read the following and answer any four questions from (i) to (v) given below:
During teaching about various environmental factors, a teacher draw a figure that depicts like history strategies for three plant species (X, Y and Z) along 3 axes - strength of competition with other organisms, level of disturbance in the habitat and level of environmental stress in the habitat. Species X grows in habitats where competition among species is high but disturbance and stress are low. Species Y grows in habitats with high environmental stress but with low intraspecies competition. Species Z grows in highly disturbed habitats with low environmental stress.

1. Which of the following is correct regarding plant type X?

1. It has slow growth rate.
2. It lives in area with high probability of severe environmental changes.
3. It has good competitive ability at low population densities near the carrying capacity.
4. None of these.

2. Environmental stress occurs through.

1. Very low temperature.
2. Drought.
3. Nutrient deficiency.
4. All of these.

3. Select the correct option regarding plant type X, Y and Z.

1. X type of plants are likely to be trees.
2. Y type of plants could be desert plants.
3. Z type of plants could be herbaceous plant.
4. All of these.

4. Y type of plants grow under high stress and:

1. Produce large number of seeds in a short time after rains.
2. Have rapid growth.
3. Produce less number of seed in a long time after rain.
4. Both (a) and (b).

5. Assertion: Plant growth rate is high in area of high stress and high disturbance.

Reason: High stress and high disturbance promote breeding capacity in plants.

1. Both assertion and reason are true and reason is the correct explanation of assertion.
2. Both assertion and reason are true but reason is not the correct explanation of assertion.
3. Assertion is true but reason is false.
4. Both assertion and reason are false.

Distinguish between : Primary and secondary succession.

Distinguish between: Homologous organs and Analogous organs.

Read the following and answer any four questions from (i) to (v) given below:
The pollen grains or microspores are the male reproductive bodies of a flower and are contained in the pollen sac or microsporangia. Each pollen grain consists of a single microscopic cell, possessing two coats: the exine and the in tine. The exine of a pollen grain is made of chemically stable material. Because of this, pollen grains are often very well preserved for thousands of years in soil and sediments.

1. One of the most resistant biological material present in the exine of pollen grain is:

1. Pectocellulose.
2. Sporopollenin.
3. Suberin.
4. Cellulose.

2. The exine possesses one or more thin places known as:

1. Raphe.
2. Germ pores.
3. Hilum.
4. Endothecium.

3. What is the function of germ pore?

1. Emergence of radicle.
2. Absorption of water for seed germination.
3. Initiation of pollen tube.
4. All of these.

4. What is the key advantage to the plant for having such strong pollen grain walls?

1. It protects the vital genetic material in the pollen grain.
2. It allows pollen to serve as a valuable fossil record for the study of ancient plants.
3. It prevents the pollen tube from growing out before the pollen grain reaches the stigma of a compatible species.
4. It gives weight to the pollen grain, allowing it to cling better to the body surfaces of insect pollinators.

5. The number of germ pores in dicots and monocots respectively are:

1. One and three.
2. Three and two.
3. Two and three.
4. Three and one.

Read the following and answer any four questions from (i) to (v) given below:
A typical angiospermic ovule is a small structure attached to the placenta by means of a stalk called funicle. The body of the ovule fuses with funicle in the region called hilum. Each ovule has one or two protective envelopes called integuments. Integuments encircle the nucellus except at the tip where a small opening called the micropyle is formed. Mature ovules are classified on the basis of funiculus. It can be orthotropous, anadromous, hernitropous, campylotropous, etc.

1. The body of the ovule consists of a mass of parenchymatous cells called:

1. Integuments.
2. Nucellus.
3. Hilum.
4. Funiculus.

2. Refer to the given figure and select the correct statement regarding it.

1. This type of ovule is found in cactus.
2. The micropyle comes to lie close to the funiculus due to unilateral growth of ovule.
3. It is most common type of ovule found in the members of Chenopodiaceae.
4. It is half inverted ovule.

3. Identify the parts labelled as A, B, C and D in the given figure and select the correct option.

S. No	A	B	C	D
(a)	Chalaza	Female gametophyte	Embryo sac	Micropyle
(b)	Chalaza	NuceIIus	Embryo sac	Micropyle
(c)	Micropyle	Egg	Embryo sac	Chalaza
(d)	Micropyle	Nucellus	Embryo sac	Chalaza

4. Mature ovules are classified on the basis of funiculus. If micropyle lie close to the funiculus, the ovule is termed as:

1. Orthotropous.
2. Anatropous.
3. Hemitropous.
4. Campylotropous.

5. In Asphodel us, ovule is:

1. Unitegmic.
2. Tritegmic.
3. Bitegmic.
4. Ategmic.

Distinguish between: Asexual Reproduction – Sexual Reproduction

Distinguish between: Spermatogenesis and Oogenesis.