Biodiversity and Conservation — BIOLOGY STD 12 Science — Question

Read the following text carefully and answer the questions that follow:
Gene regulation is the mechanism of switching off and switching on of the genes depending upon the requirement of cells and the state of development. Gene regulation is of two types: negative and positive. In negative gene regulation, the genes continue expressing their effect till their activity is suppressed. Positive gene regulation is the one in which the genes remain non-expressed unless and until they are induced to do it. Operon model is a co-ordinated group of genes such as structural gene, operator gene, promoter gene, regulator gene which function together and regulate a metabolic pathway as a unit, e.g., lac operon, trp operon, ara operon, etc.

i. Regulation of gene expression occurs at which the level? (1)
ii. What is complementary to an mRNA molecule transcribed from the lac operon contains nucleotide sequences? (1)
iii. Describes the control of transcription of the genes involved in the breakdown of lactose in Escherichia coli?
(2)
OR
What is the function of catabolic activator protein in lac operon? (2)

Read the following and answer any four questions from (i) to (v) given below:

The mature ovum or a female gamete is spherical in shape. The human ovum is almost free of yolk and is said to be alecithal. Human ovum loses its ability to be fertilised about 24 hours after ovulation. Refer to the given structure of ovum and answer the following questions.

1. Thick cellular layer formed of radially elongated follicular cells is:

1. Zona pellucida.
2. Plasma membrane.
3. Perivitelline membrane.
4. Corona radiata.

2. In humans, at which stage does ovum get released from ovary?

1. Secondary oocyte.
2. Oogonium.
3. Primary oocyte.
4. First polar body.

3. Cytoplasm of an ovum is enveloped by _____.

1. Zona pellucida.
2. Corona radiata.
3. Cell membrane.
4. Perivitelline space.

4. Select the correct option:

S. No	V	W	X
(a)	Cytoplasm	Zona pellucida	Plasma membrane
(b)	Cortical granules	Corona radiata	Zona pellucida
(c)	Cortical granules	Plasma membrane	Corona radiata
(d)	Cytoplasm	Corona radiata	Zona pellucida

5. Which of the following is not a characteristic of an ovum?

1. Nucleus of an ovum has prominent nucleolus.
2. Only one ovum formed from one oogonium.
3. It lacks centrioles.
4. It has very small amount of ooplasm.

Describe tissue culture.

Read the following and answer any four questions from (i) to (v) given below:
The foundations of recombinant DNA (rDNA) were laid by the discovery of restriction enzymes. These enzymes are present in many bacterias where they function as a part of their defense mechanism called the Restriction Modification system (RM system). Molecular basis of this system was explained first by Werner Arber in 1962. The Restriction Modification system consists of two components:

• A restriction enzyme (called restriction endonuclease) identifies the introduced foreign DNA and cuts it into pieces.
• The second component is a modification enzyme (methylase) that adds a methyl group to DNA at specific site to protect it from the restriction enzyme cleavage.

1. Restriction endonucleases are enzymes present in ________ where they function as a part of _______ mechanism.

1. (i) bacteria (ii) digestive
2. (i) protists (ii) transcription
3. (i) plant cells (ii) replication
4. (i) prokaryotes (ii) defence

2. Which of the following statements regarding modification enzyme is correct?

1. It adds methyl group to one or two bases usually within the host DNA sequence to protect it from the restriction enzyme.
2. It adds ethyl group to one or two bases usually within the sequence recognised by the restriction enzymes.
3. It adds methyl group to only one of bases within the foreign DNA sequence that is recognised by the restriction enzymes.
4. None of these.

3. Which of the following is a type II restriction enzyme?

1. Alu I
2. EcoR I
3. BamH I
4. All of these.

4. Which of the following is the first discovered restriction endonuclease?

1. Sal I
2. EcoR I
3. Hind II
4. EcoR II

5. Components of Restriction Modification System include?

1. Restriction enzyme.
2. Modification enzyme.
3. Lysing enzyme.
4. Both (a) and (b).

Read the following text carefully and answer the questions that follow:
A pathogen is defined as an organism causing disease to its host, with the severity of the disease symptoms referred to as virulence. Pathogens are taxonomically widely diverse and comprise viruses and bacteria as well as unicellular and multicellular eukaryotes. The immune system of a person is suppressed. He was found positive for a pathogen in the diagnostic test ELISA.

i. Name the disease, the patient is suffering from. (1)
ii. Which pathogen is identified by ELISA test? (1)
iii. Which cells of the body are attacked by the pathogen? (2)
OR
Suggest preventive measures of the infection. (2)

Read the following and answer any four questions from (i) to (v) given below:

Ananya is a biologist, her research guide assigned project, i.e., to determine the effect ofin tra-specific competition on the growth of sapling of Eucalyptus. For this, she designed an experiment in which two sets of pots were used. ln the first set (set A) only I sapling was planted per pot and in the other set (set B) 16 saplings were planted per pot. To check for the effect of intra-specific competition on allocation of resources, a decreasing amount of water was added to each set. The results have been graphically indicated. Which of the following conclusions can indicated as follows:

1. Which of the following statements can be concluded from the given study?

1. More resources are allocated to the root during low water conditions.
2. Competition for water among individuals of a population causes more root growth as compared to individuals who are growing alone.
3. Lesser leaves are formed under low water conditions.
4. Root growth is higher in individual grown singly as compared to individuals in populations.

2. Which of the following associations is an example of competitions?

1. Cuscuta and hedge plant.
2. Balanus and Cathamalus.
3. Cactus and moth.
4. Orchid and mango.

3. If '+' sign is assigned to beneficial interaction, '-' sign to detrimental and O sign to neutral interaction, then the population interaction of competition refers to:

1. +, +
2. -, -
3. +, -
4. +, 0

4. lntraspecific competition is more severe due to:

1. similar needs.
2. similar adaptations.
3. common resources.
4. all of these.

5. Assertion: Two members of a competing species may co-exist.

Reason: Different individuals of a species have different resource requirements.

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.

Read the following and answer any four questions from (i) to (v) given below:

Unlike animals, plants cannot runaway for their defence, therefore, they have evolved an astonishing variety of morphological and chemical defences against herbivores. Thorns are the most common morphological means of defence. Many plants produce and store chemicals that make the herbivore sick when they are eaten, inhibit feeding or digestion, disrupt its reproduction or even kill it. Some plants produce highly poisonous chemicals and that is why no cattle or goats browse on those plants. A wide variety of chemical substances that we extract from plants on a conunercial scale are produced by them actually as defence against grazers and browsers.

1. Why you never see cattle or goats browsing on weed Calotropisl?

1. It produces highly poisonous tannins.
2. It produces quinine which is bitter in taste.
3. It produces poisonous cardiac glycosides.
4. It bears prickles.

 

2. What could be the possible reason for invasive growth of the prickly pear cactus introduced in Australia?

1. Absence of predators.
2. New mycorrhizal association.
3. Abundant water availability.
4. All of these.

3. Which of the following is most likely to sick by consuming chemicals produced by plants?

1. Frog
2. Goat
3. Human
4. Pigeon

4. Plant evolve variety of morphological and chemical defences against.

1. Prey
2. Predator
3. Commenal
4. Mutualist

5. Assertion: Some plant functions as predator in nature.

Reason: Phytoph ago us insects feed on plant sap.

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.

Give information about primary and secondary lymphoid organ ### Explain lymphatic organs of human lymphatic system. (Diagram is not required)

Read the following text carefully and answer the questions that follow:
Cleavage is the series of rapid mitotic divisions in zygote and forms blastula. The 2, 4, 8, 16 daughter cells are called blastomeres. Embryo with 64 blastomeres is known as blastocyst and has blastocoel cavity. Blastocyst gets implanted in uterine wall and leads to pregnancy.
i. Why the cells of the inner cell mass of blastocyst are called stem cells? (1)
ii. At which stage of embryonic development trophoectoderm develops? (1)
iii. What is the site of implantation? (2)
OR
What is the correct sequence of various structures formed during embryonic development? (2)