Solution

PERIODIC TEST-III

Class 11 - Biology
Section A
1. (a) Abbreviated
Explanation:
The name of the author appears after the specific epithet, i.e., at the end of the biological name and is written in an abbreviated
form, e.g., Mangifera indica Linn. It indicates that this species was first described by Linnaeus. Hence, the correct option is
Abbreviated.
2.
(d) Family
Explanation:
Plant families like Convolvulaceae, Solanaceae are included in the order Polymoniales mainly based on the floral characters.
Hence, the correct option is Family.

3.
(d) Methanogens
Explanation:
Methanogens are present in the guts of several ruminant animals such as cows and buffaloes and they are responsible for the
production of methane (biogas) from the dung of these animals.

4. (a) Cell wall

Explanation:
The cell wall of fungi is made up of chitin while the green plants had a cellulosic cell wall. Due to this, fungi were placed in a
separate kingdom – Kingdom Fungi.
5.
(d) Outside the body
Explanation:
In amphibians, syngamy occurs in the external medium (water) i.e. outside the body of organisms while in reptiles, syngamy
occurs inside the body of an organism.

6.
(d) Singer and Nicolson
Explanation:
Singer and Nicolson in 1972. It is the most widely accepted model. According to this, biological membranes are quasi fluid
structures in which lipids and proteins are arranged in a mosaic manner.

7. (a) PPLOs
Explanation:
Pleuro Pneumonia Like Organism (PPLO) or mycoplasma is considered as the smallest free-living organism.
8.
(d) 9
Explanation:
The 9 essential amino acids are histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and
valine.

9.
(c) Water
Explanation:

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 Water is the most abundant component of living organism, made up of hydrogen and oxygen.

10.
(d) Golgi apparatus
Explanation:
Synthesis of glycoproteins and glycolipids take place in Golgi apparatus inside the cell. Golgi apparatus is located near the
nucleus of the cell.

11.
(b) Metaphase
Explanation:
The metaphase is characterized by all the chromosomes coming to lie at the equator with one chromatid of each chromosome
connected by its kinetochore to spindle fibres from one pole and its sister chromatid connected by its kinetochore to spindle
fibres from the opposite pole.

12.
(d) Increasing the number of chromosome sets
Explanation:
Polyploidy is the condition in which more than one set of chromosomes is present in one cell. It is the property of increasing
the number of chromosome sets of the cell and results due to the failure of the segregation of non-sister chromatids after
crossing over.

13. (a) Both A and R are true and R is the correct explanation of A.
Explanation:
International Code of Botanical Nomenclature (ICBN) is responsible for giving a scientific name to plants. It uses articles,
photos and recommendations to plant.
14.
(d) A is false but R is true.
Explanation:
Sclerospora graminicola causes downy mildew of cereals. Pernospora parasitica causes downy mildew of crucifers and
Plasmopara viticola causes downy mildew of grapes.

15. (a) Both A and R are true and R is the correct explanation of A.
Explanation:
With the increase in substrate concentration, the velocity of the enzymatic reaction rises at first and ultimately reaches a
maximum velocity which is not exceeded by any further rise in the concentration of the substrate because the enzyme
molecules are fewer than the substrate molecules and after saturation of these molecules, there are no free enzyme molecules to
bind with the additional substrate molecules.
16.
(d) A is false but R is true.
Explanation:
Crossing over is a process of the exchange of genetic material or chromatid segments between two homologous chromosomes.
Recombination occurs between two of the chromatids of each homologue. When the homologous paternal and maternal
chromosomes separate in anaphase, two of their chromatids are mixed, the other two maintain their initial nature.

Section B
17. Protozoans take in water in bulk. As they mostly live in aquatic environments. They are highly likely to burst due to excessive
intake of water. Therefore, protozoans need to osmoregulate continuously to keep only the required amount of water in their cells.
They get rid of excess water through contractile vacuoles.
18. The canals connect the spongocoel to the outside through the Ostia. The canals are generally lined by choanocytes. The
continuous beating of flagella of choanocytes maintains a steady current of water through the canals.

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19. Glycocalyx is significant in the following ways
i. It protects the cell from loss of water and nutrients.
ii. Serves as a protective layer against attack by phagocytosis and viruses.
iii. Helps in attachment to a surface.
iv. Provides virulence.
OR
Intracellular digestion takes place by the action of lysosomes. The lysosomes possess the digestive enzymes (hydrolases) which
are produced in the rough endoplasmic reticulum and stored in the Golgi apparatus.

20. Ligases Lyases

These are the enzymes which catalyse the covalent These are the enzymes which catalyse the cleavage of specific covalent
bonding between two substrates to form a large bonds in a large molecule to form smaller molecules without the addition
molecule. of water.
OR
Line B will show the rate of reaction at 60oC because the rate of reaction initially is more rapid but then decreases as the enzyme
becomes denatured by the high temperature. Thus, the quantity of product remains constant at a lower amount compared to line N.
21. i. Zygotene
ii. Pachytene
iii. Telophase - I/After Meiosis - I
iv. Diakinesis
Section C
22. Phylum. Phylum comes next to Kingdom in the taxonomical hierarchy. All broad characteristics of an animal or plant are defined
in a phylum. For example all chordates have a notochord and gill at some stage of life cycle. Similarly all arthopods have joined
legs made of chitin.
Order. Order further zeroes down on characteristics and includes related genus. For example humans and monkeys belong to the
order primates. Both humans and monkeys can use their hands to manipulate objects and can walk on their hind legs.
Genus. Comprises a group of related species which has more characters in common in comparison to species of other genera. We
can say that genera are aggregates of closely related species. For example, potato, tomato and brinjal are three different species
but all belong to the genus Solanum. Lion (Panthera leo), Leopard (P. pardus) and tiger (P. tigris) with several features, are all
species of the genus Panthera. This genus differs from another genus Felis which includes cats.
Species. Taxonomic studies consider a group of individual organisms with fundamental morphological similarities as a species .
One should be able to distinguish one species from the other closely related species based on he distinct morphological
differences.
23. i. Difference between Lichen and Mycorrhiza are:

Lichen Mycorrhiza

mycorrhizae are a symbiotic association between a fungus and a

Lichens are a symbiotic association between algae and fungi.
plant.

Lichens can grow on many surfaces, including trees, rocks, Mycorrhizal fungi live in the interface between the soil and the
soil, houses, etc. plant's roots.
Lichens are made up of algae that produces food through Mycorrhizae help plants get more nutrients and water, especially
photosynthesis, and a fungus that absorbs water and minerals phosphorus. Mycorrhizal fungi also play a role in soil biology
for the algae. and chemistry.

ii. Difference between A Basidium and Ascus are:

A basidium An ascus

A club-shaped structure found in basidiomycetes fungi. An ascus is a bag-like structure found in ascomycetes fungi.

Basidiospores are produced in the basidium. Ascospores are produced in the ascus.
24. The presence or absence of the body cavity gives a clue about a particular animals position in evolutionary ladder. The absence of
coelom indicates that the animal is yet to develop a functional division of labour to carry out various activities.

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 This indicates towards a simplicity of activities going on inside the body. The presence of coelom paves the way for evolution of a
more complex and more efficient organ system for various activities.
OR
Direct Development. In direct development the young animal resembles an adult.
There is no intermediate stage.
Indirect Development. In indirect development there is intermediate stage, like larval stage. For example, frogs before being
developed into adult pass through a tadpole stage. This is the case of indirect development.
25. The fluid mosaic model was proposed in 1972 by Singer and Nicolson. It's one of the dominant models of cell membrane structure
today.
The fluid mosaic model describes the structure of a cell membrane as a two-dimensional liquid with a fluid bilayer of
phospholipids and embedded proteins:
Phospholipid bilayer: A two-molecule thick layer of phospholipids with hydrophilic heads facing outwards and hydrophobic
tails facing inwards. The phospholipid bilayer gives the membrane fluidity and elasticity.
Proteins: Globular integral membrane proteins are embedded in the fluid lipid bilayer. These proteins can extend partway into the
membrane, cross the membrane entirely, or be loosely attached to its inside or outside face.
Carbohydrates: Small amounts of carbohydrates are found on the outer surface of the plasma membrane. They are attached to
proteins, forming glycoproteins, or lipids, forming glycolipids.
Cholesterol: Another lipid composed of four fused carbon rings, is found alongside phospholipids in the core of the membrane.

26. i. The type of inhibition of succinic dehydrogenase by malonate is competitive inhibition.

ii. The inhibitor competes with the substrate for the active sites of enzyme molecules as it has a structure similar to the substrate
that allows it to combine with the active site, preventing any substrate molecule from occupying that site. This reduces the rate
of the reaction since, the substrate can only use the enzyme molecules that are not occupied by the inhibitor, resulting in the
same quantity of product being formed at a slower rate.
27. Most of the enzymes function in a narrow range of pH, that is, each enzyme shows its highest activity at a particular optimum pH.
Thus, their activity declines both below and above the optimum value. The graph shows the maximum enzyme activity at the
optimum pH. The rate of enzyme activity decreases above and below that optimum pH.

ii. Enzymes are proteins that have many important properties, including:
1. Catalytic: Enzymes are catalysts that can increase the rate of a reaction by lowering the activation energy.
2. Substrate specificity: Enzymes are highly specific to a particular substrate.
3. Heat sensitive: Enzymes are very sensitive to heat and temperature. Enzyme activity is highest at an optimum temperature
(20°-30°C), increase in temp denature the protein nature .
4. Enzyme concentration: The number of enzymes present in an area is called the enzyme concentration. Changing the
concentration of enzymes can change the rate of the reaction.
28. The mitosis has 4 stages :
i. Prophase,
ii. Metaphase,
iii. Anaphase,
iv. Telophase.
The chromosomes condense during prophase. Centrioles move to opposite poles. Nuclear envelope, as well as the nucleolus,
disintegrate. Spindle fibres begin to appear. At metaphase alignment of chromosomes at equatorial plate occurs. Centromeres
divide and the chromatids begin to move towards two opposite poles at anaphase. Chromatids reach 2 poles, chromosomal
elongation begins. The nucleolus, as well as nuclear membrane, reappear at telophase. Then nuclear division is followed by
cytoplasmic division (cytokinesis). Hence, the mitosis is called equational division and number of chromosome in the parent and
the daughter cell remains the same.
Section D

29. i. Prokaryotic cells Eukaryotic cells

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 In prokaryotic cells, the cell wall is present and it is very Eukaryotic cells have cell walls very rarely, if present they have
complex in nature. simple chemical nature.

DNA is arranged in a circular shape DNA is linear in shape.

ii. The cell envelope in prokaryotes consists of a tightly bound three-layered structure i.e., the outermost glycocalyx followed by
the cell wall and then the plasma membrane.
iii. A special membranous structure called mesosome is formed by the extensions of the plasma membrane into the prokaryotic
cell.
OR
Chloroplasts and mitochondria which have doble membrane.
30. i. In metaphase, the microtubules start pulling the chromosomes with equal force and the chromosome ends up in the middle of
the cell. This region is known as the metaphase plate. Thus, each cell gets an entire functioning genome.
ii. Kinetochores are Small disc-shaped structures at the surface of the centromeres, which serve as the sites of attachment of
spindle fibres to the chromosomes that are moved into position at the centre of the cell.
iii. The completion of prophase is marked by the following characteristic events:
Chromosomal material condenses to form compact mitotic chromosomes. Chromosomes are seen to be composed of
two chromatids attached together at the centromere.
Centrosome which had undergone duplication during interphase, begins to move towards opposite poles of the cell.
Each centrosome radiates out microtubules called asters. The two asters together with spindle fibres forms mitotic
apparatus.
OR
Karyokinesis involves following four stages: Prophase, Metaphase, Anaphase, Telophase
Section E
31. Structures responsible are
i. Smooth endoplasmic Reticulim (SER) is responsible for the manufacture of lipids and steroids.
ii. Mitochondrion is responsible for the release of energy.
iii. Ribosomes are responsible for the production of hormones and digestive enzymes.
iv. Centrioles are responsible for production of spindle fibres.
v. Plasma membrane is responsible for endo and exocytosis.
OR
Plastids are found in all plant cells and in euglenoids. These are easily observed under the microscope as they are large. They bear
some specific pigments, thus imparting specific colours to the plants. Based on the type of pigments plastids can be classified into
chloroplasts, chromoplasts and leucoplasts.
i. Chloroplasts: The chloroplasts contain chlorophyll and carotenoid pigments which are responsible for trapping light energy
essential for photosynthesis.
ii. Chromoplasts: In the chromoplasts fat-soluble carotenoid pigments like carotene, xanthophylls and others are present. This
gives the part of the plant a yellow, orange or red colour.
iii. Leucoplasts: The leucoplasts are the colourless plastids of varied shapes and sizes with stored nutrients: Amyloplasts store
carbohydrates (starch), e.g. potato elaioplasts store oils and fats whereas the aleuroplasts store proteins.
iv. Shape and Size of Chloroplasts: Majority of the chloroplasts of the green plants are found in the mesophyll cells of the
leaves. These are lens-shaped, oval, spherical, discoid or even ribbon-like organelles having variable length (5-10 nm) and

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 width (2-4nm). Their number varies from 1 per cell of the Chlamydomonas, a green alga to 20-40 per cell in the mesophyll.

v. Structure of Chloroplasts: Like mitochondria, the chloroplasts are also double membrane-bound. Of the two, the inner
chloroplast membrane is relatively less permeable. The space limited by the inner membrane of the chloroplast is called the
stroma. A number of organised flattened membranous sacs called thylakoids are present in the stroma. Thylakoids are
arranged in stacks like the piles of coins called grana (singular: granum) or the internal thylakoids. In addition, there are flat
membranous tubules called the stroma lamellae connecting the thylakoids of the different grana. The membrane of the
thylakoids encloses a space called a lumen. The stroma of the chloroplast contains enzymes required for the synthesis of
carbohydrates and proteins. It also contains small, double-stranded circular DNA molecules and ribosomes. Chlorophyll
pigments are present in the thylakoids. The ribosomes of the chloroplasts are smaller (70 S) than the cytoplasmic ribosomes
(80 S).
32. Mechanism of Enzymatic Action
i. Enzymes act by lowering the activation energy of reactions by creating an environment in which the transition state is
stabilized (e.g. straining the shape of a substrate by binding the transition-state conformation of the substrate/ product
molecules, the enzyme distorts the bound substrate(s) into their transition state form, thereby reducing the amount of energy
required to complete the transition).
ii. Lowering the energy of the transition state, but without distorting the substrate, by creating an environment with the opposite
charge distribution to that of the transition state.
iii. Providing an alternative pathway: For example, temporarily reacting with the substrate to form an intermediate ES complex,
which would be impossible in the absence of the enzyme.
iv. Reducing the reaction entropy change by bringing substrates together in the correct orientation to react. Considering ΔH +
+

alone overlooks this effect.

v. Increase in temperature speeds up reactions. Thus, temperature increase helps the enzymes function and develop the end
product even faster. However, if heated too much, the enzyme's shape deteriorates and only when the temperature comes back
to normal does the enzyme regains its original shape. Some enzymes like thermolabile enzymes work best at low
temperatures.
The catalytic cycle of an enzyme action can be described in the following steps:
i. First, the substrate binds to the active site of the enzyme.
ii. The binding of the substrate induces the enzyme to alter its shape (conformational change), fitting more tightly around the
substrate.
iii. The active site of the enzyme, now in close proximity of the substrate breaks the chemical bonds of the substrate and the new
enzyme - product complex is formed.
iv. The enzyme releases the products of the reaction and the free enzyme is ready to bind to another molecule of the substrate and
run through the catalytic cycle once again.
OR
Structure of protein
Primary Structure . The sequence of amino acids i.e., the positional information in a protein is called the primary structure of a
protein. A protein is imagined as a line, the left end represented by the first amino acid and the right end represented by the last
amino acid. The first amino acid is also called as N-terminal amino acid. The last amino acid is called the C-terminal amino acid.
A protein thread does not exist throughout as an extended rigid rod.
Secondary Structure. Regularly repeating local structures stabilized by hydrogen bonds. The most common examples are the
alpha helix, beta sheet and turns. Because secondary structures are local, many regions of different secondary structures can be

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 present in the same protein molecule.
Tertiary structure. The overall shape of a single protein molecule-- the spatial relationship of the secondary structures to one
another represents tertiary structure. Tertiary structure is generally stabilized by non-local interactions, most commonly the
formation of a hydrophobic core, but also through salt bridges, hydrogen bonds, disulfide linkages and even post-translational
modifications. The term "tertiary structure" is often used as synonymous with the term fold. The Tertiary structure is what controls
the basic function of the protein.
Quaternary Structure. Some proteins are an assembly of more than one polypeptide chain or subunits. The manner in which
these individual folded polypeptides or subunits are arranged with respect to each other (e.g. linear string of spheres, spheres
arranged one upon each other in the form of a cube or plate etc.) is the architecture of a protein otherwise called the quaternary
structure of a proteins.
33. Following are the various stages of meiotic prophase - I:

i. Leptotene: During this stage, chromosomes become gradually visible under the light microscope. The compaction of the
chromosome continues through this stage. The sister chromatids are so tightly bound that one cannot be differentiated from
another.
ii. Zygotene: At this stage, chromosomes start forming pairs. This process is called synapsis. Formation of synapsis is
accompanied by the formation of synaptonemal complex. Each pair is called a bivalent or tetrad.
iii. Pachytene: At this stage, the bivalent chromosomes become distinct. Recombination nodules appear on the tetrads. The
recombination nodule is the site at which crossing over takes place. Crossing over takes place between non-sister chromatids
of homologous chromosomes. Crossing over facilitates the exchange of genes between two homologous chromosomes.
iv. Diplotene: At this stage, the synaptonemal complex gets dissolved. The recombined chromosomes begin to separate from
each other. But they are attached at the site of crossing over. This makes an X-shaped structure called chiasmata.
v. Diakinesis: Chiasmata is terminated at this stage. The nucleolus disappears and so does the nuclear membrane.
OR
Cell Cycle:
The cell cycle is an orderly sequence of events or a set of stages by which a cell duplicates its genome, synthesises the other
constituents (important for the cell) of the cell and eventually divides into two daughter cells.
Interphase:
It is the period between the end of one cell division to the beginning of the next cell division, i.e., (between two successive M-
phase).
During this phase, the cell prepares itself for both cell growth and DNA replication in an orderly manner. So, it is also known as
the preparation phase. It lasts for about 90-96%, i.e., more than 95% of the total duration of the cell cycle. In a cell cycle of
human cell, only about one hour is taken by the dividing phase out of 24 hours duration of one cell cycle.
Interphase is further divided into following three substages on the basis of various synthetic activities
i. G1(Gap-1)-phase
It corresponds to the duration between the mitosis (M-phase) and initiation of replication of DNA. The cell becomes
metabolically very active during this period. It grows continuously and prepares itself for DNA replication. Thus synthesising
enzymes and proteins needed for this process.
ii. S (Synthesis)-phase
It is known to be the phase in which actual synthesis or replication of DNA takes place. The overall amount of DNA doubles
per cell, but no increase in chromosome number takes place during this phase. If the initial amount of DNA is 2C, it will

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 become 4C.
In the case of an animal cell, during S-phase DNA replication begins inside the nucleus while the duplication of centrioles
takes place in the cytoplasm.
iii. G2 (Gap-2)-phase This phase is also called post-synthetic or pre-mitotic phase. During this stage, the synthesis of DNA stops
and proteins required for mitosis are being synthesised while the growth of cell continues. It prepares the cell to undergo
division.

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