Biology: Topic-wise Test- 4 - NEET MCQ

Phases Of Plant Growth

1. Meristematic Phase

• The cells in the root and shoot apex of a plant are constantly dividing. They represent the meristematic phase of growth.
• The cells in these regions have large nuclei and are rich in protoplasm and their cell walls are thin and contain cellulose.

2. Elongation Phase

• The cells in the zone just after the meristematic region represent the phase of elongation.
• The characteristics of cells in this zone are cell enlargement, increased vacuole formation and new cell wall deposition.

3. Maturation Phase

• Just close to the phase of elongation, but away from the apex lies the phase of maturation.
• The cells in this region reach their maximum size with respect to their protoplasm and cell wall thickening.

Phases of Plant Growth:

Stem elongation is a kind of growth of stem.

Auxin and Gibberellin are known as growth hormones of plants. Therefore, stem elongation is affected by hormones Auxin and Gibberellin.

1. Krebs cycle is also known as the citric acid cycle because this reaction starts with the six-carbon compound which is citric acid. It occurs in the mitochondrial matrix.
2. Krebs cycle is a closed-loop cycle. And each loop of the cycle generates a molecule of ATP. This cycle consists of eight steps which include redox, dehydration, hydration, and decarboxylation reactions. It is an aerobic pathway because NADH is produced and the electrons released are used up in the next cycle which uses oxygen.
3. The process of the cycle starts with the condensation of acetyl- CoA with oxaloacetate.
4. This reaction is controlled by the amount of ATP present.
5. If the ATP level increases then the rate of the reaction decreases and vice versa. After glycolysis, the pyruvate is then converted into acetyl CoA which enters the citric acid cycle.
6. The Krebs cycle is the pathway that all organisms use to generate energy. The intermediate compound that links pyruvate to the Krebs cycle is Acetyl CoA.
7. So, the answer is option (B) ‘the intermediate compound which links glycolysis with the Krebs cycle is malic acid’.

Light is the visible part of electomagnetic radiations. Visible light consists of radiations having a wavelength between 390-760 nm (or 399-430nm), blue of indigo (430-470nm), blue green or blue (470-500nm), green (500-580nm), yellow (580-600nm), orange (600-650nm), orange red (650-600nm) and red (660-760nm).

The portion of pith taken as an explant comprises of parenchymatous cells (i.e., simple permanent tissue which have lost the capcity to divide). When such cells are cultured on solid culture media, the parenchymatous cells of pith become meristematic and start dividing resulting in a mass of undifferentiated cells called callus. this is an example of dedifferentiation. These cells may be made to divide in different manners in order to produce different organs so that the meristematic cells of callus may become permanent tissues by the process of redifferentiation. for exmaple, treatment of certain hormones may lead to the differentitation of shoot buds or roots.

RuBisCO that is the most abundant enzyme in the world and is characterised by the fact that its active site can bind to both CO₂ and O₂ hence the name.

Respiration is an oxidative process in which repiratory substrates are oxidised to liberate energy inside the living cells. The common respiratory substrates are carbohydrates, proteins, fats and organic acids. The most common respiratory substrates are carbohydrates, proteins, fats and organic acids. The most common respiratory substrate is glucose.

The organism that depends on dead and decaying organic matter is called a saprophyte. Saprophytes are a type of decomposer that obtain their nutrients and energy by breaking down dead plant or animal material. They play a vital role in the ecosystem by recycling nutrients and returning them to the environment for other organisms to use. 

Example: Moulds, Mushroom etc. 

• Autotrophs, on the other hand, are organisms that can produce their own food using inorganic substances and an external energy source, such as sunlight. They convert carbon dioxide and water into organic compounds through the process of photosynthesis (in plants) or chemosynthesis (in some bacteria). Autotrophs do not rely on dead organic matter for their nutrition.
• Carnivores are organisms that primarily consume the flesh of other animals. They obtain their energy and nutrients by hunting and feeding on other living organisms, rather than on dead organic matter.
• Herbivores are organisms that primarily consume plant material. They obtain their energy and nutrients by feeding on plants or plant parts. Herbivores generally do not depend directly on dead and decaying organic matter as their main source of nutrition.

The following are plant growth regulators or phytohormones that control various developmental as well as physiological functions of a plant:

Auxin:

• It helps in cell elongation, growth, and differentiation.
• It is present mainly at the root and shoots apices.
• It is responsible for the phenomenon of apical dominance, where the apical buds inhibit the growth of lateral buds.
• It results in increasing the height of a plant due to apical dominance.
• It can also initiate root growth in stem cuttings.
• It may also promote flowering and prevent early fruit drop.

Cytokinin:

• It is mainly associated with cell division and is present in regions of rapid cell division.
• It helps to overcome apical dominance and promotes lateral shoot growth.

Ethylene:

• It is a gaseous phytohormone produced in the tissues undergoing senescence.
• It helps in fruit ripening and other senescence-related activities.
• It breaks seed and bud dormancy to initiate germination in some species.
• It also induces leaf epinasty under stress conditions.
• The triple response of ethylene includes reducing the rate of elongation, increasing lateral expansion, and swelling of the region below the hook in seedlings.

Abscisic acid:

• As the name suggests, it helps in abscission and dormancy.
• It inhibits plant growth, metabolism, and seed germination.
• It also plays an important role in the closure of stomata under stress conditions.

Parthenocarpy (literally meaning "virgin fruit") is the natural or artificially induced production of fruit without fertilization of ovules, which makes the fruit seedless. 

It may also produce apparently seedless fruit, but the seeds are actually aborted while they are still small. 

Phosphofructokinase is a kinase enzyme that phosphorylates fructose-6-phosphate in glycolysis. The enzyme catalysed transfer of a phosphoryl group from ATP is an important reaction in a wide variety of biological processes.

(A) Auxin - (IV) Promotes flowering in pineapple: Auxins are a class of plant hormones that influence cell growth by altering cell elongation. However, the role of promoting flowering in pineapple is actually played by Ethylene. Therefore, there's an error in this match.

(B) Gibberellin - (III) Increase in the length of grape stalks: Gibberellins are plant hormones that stimulate stem elongation, seed germination, and flowering. They are known to increase the length of grape stalks.

(C) Cytokinin - (II) Overcoming apical dominance: Cytokinins are plant hormones that promote cell division and delay leaf senescence. They also play a role in overcoming apical dominance, encouraging the growth of lateral buds.

(D) Ethylene - (I) Promotes female flower formation in cucumber: Ethylene is a gaseous plant hormone which regulates a wide range of biological processes. It is known to influence sex determination in certain plants, promoting female flower formation in cucumber.

Absolute growth rate (AGR): Increase in total growth of two organs or organisms is measured and comparison of total growth per unit time is called absolute growth. Absolute growth rate is the total growth per unit time. Relative growth rate (RGR) : It is growth per unit time per unit initial growth.
RGR= Growth in given time period / Measurement at start of time period
AG for leaf A = 10cm² = 5cm² = 5cm²
RGR for leaf A = 5/5 ​× 100 = 100%
AG for leaf B = 55cm² − 50cm² = 5cm²
RGR for leaf B = 5/50 ​× 100 = 10%
Though the absolute growth is same for both the leaves (A and B), relative rate of growth is more in leaf A because of its initial small size.

The TCA cycle begins with a condensation reaction. In this step, an acetyl group, derived from the breakdown of glucose or fatty acids, combines with oxaloacetic acid (OAA), a four-carbon molecule, in the presence of water. This condensation reaction forms a six-carbon compound called citric acid or citrate.

The complete reaction is as follows:
Acetyl-CoA + OAA + H₂O → Citric Acid (Citrate)

The condensation step is significant because it marks the entry of the acetyl group into the TCA cycle and the beginning of a series of enzymatic reactions that ultimately lead to the release of energy and the regeneration of OAA.

Because the respiratory pathway is involved in both anabolism and catabolism, it would hence be better to consider the respiratory pathway as an amphibolic pathway rather than as a catabolic one.

Photosynthesis takes place in the green leaves of plants and other green parts of plants like stem etc. The most active photosynthetic tissue in higher plants is the mesophyll of leaves. Mesophyll cells have many chloroplasts, which contain the specialized light-absorbing green pigments, the chlorophylls. When chlorophyll absorbs light, it gets excited and emits electrons. These chlorophylls are found in photosynthetic units called Photosystem I and Photosystem II. Each unit has a specific reaction centre which contains pigment molecules. These molecules absorb light of different wavelengths and emit electrons. Due to the photon of light, electrons of chlorophyll get excited. These electrons are picked up by an electron acceptor which passes them to an electron transport system of cytochromes. The excitement of electrons of chlorophyll b photon of light is the first step of photosynthesis.

Fermentation is a kind of anaerobic respiration in absence of oxygen to produce ethanol and carbon dioxide gas. Dough kept overnight in warm place becomes soft and spongy due to carbon dioxide gas released during fermentation.

The C₄ plants respond to higher temperatures and show higher rate of photosynthesis while C₃ plants have a much lower temperature optimum.

Ruben and Kamen (1941), while working on chlorella (unicellular green alga ) found that oxygen liberated during photosynthesis comes from water. 

(i) When normal H₂​O radioactive CO₂​(i.e.CO₂¹⁸​) were used, normal O₂​ is evolved. 

(ii) When normal CO₂​ radioactive H₂​O(i.e.H₂​O¹⁸) were used, radioactive O₂​ (i.e.O₂^18​) is evolved. 

nCO_2​+nH_2​O¹⁸→(CH₂​O)n​+O₂¹⁸​↑ (radioactive oxygen)+H₂​O 

So the correct option is 'D'.

The Lateral meristem e.g. vascular cambium and  cork cambium(in dicotyledons and gymnosperms) are the meristems that cause increase in girth of the organs in which they are active, This is known as secondary growth of the plant.

Mitochondria (singular - Mitochondrion) are known as the powerhouse of the cell because they are responsible for the release of energy from food ,i.e, cellular respiration. This energy is released in the form of ATP (adenosine triphosphate), the energy currency of the cell.

While the cells release 2 ATP, mitochondria releases 34 ATP which adds up to 36 ATP. Since a major portion of the ATP is released by mitochondria, they are called the powerhouse of the cell.

Photophosphorylation is the process in which ATP is produced, which is called as energy currency of the cell. During this process, ADP is phosphorylated to give ATP in presence of light energy.
So, the correct answer is option B.

During breakdown and synthesis of protein too, respiratory intermediates form the link. Breaking down processes within the living organism is catabolism, and synthesis is anabolism. Because the respiratory pathway (Kreb’s cycle) is involved in both anabolism and catabolism, it would hence be better to consider the respiratory pathway.

The reason of algae float to the surface during the day & sink at night is due to photosynthesis. In Day time, the algae is producing oxygen. When enough Oxygen is produced during the day , it gets trapped in bubbles and it can lift the clumps up to the surface.

• Cytokinin does not help in promoting leaf senescence.
• Cytokinin production slows down the process of senescence. However, the accumulation of sugars during senescence, due to the breakdown of accumulated starch or the preferential export of N₂ from the leaf, can block the effect of cytokinin, especially in low light.
• Ethylene is regarded as a multifunctional phytohormone that regulates both growth, and senescence.
• It promotes or inhibits growth and senescence processes depending on its concentration, timing of application, and the plant species.

In chloroplast there is the membranous system consisting of grana, the stroma lamellae, and the fluid stroma. There is a clear division of labour within the chloroplast. The granum is responsible for trapping the light energy.

A meristematic tissue is a group of similar and immature cells that are in continuous state of division. These tissues are found in growing regions of plants. The chief characteristics of these tissues are:
(i) The cells may be round, oval, polygonal or rectangular.
(ii) They have thin cellulosic cell walls.
(iii) They do not have intercellular spaces.
(iv) They have dense cytoplasm with prominent nuclei.
(v) Vacuoles are absent or many small vacuoles may be present. The cells are in active state of metabolism.

Growth, at a cellular level, is principally a consequence of increase in the amount of protoplasm. Growth is measured by a variety of parameters such as  (i) increase in length, e.g, stem,root, pollen tube (ii) increase in volume eg., fruits. (iii) Increase in area, eg.leaves (iv) increase in diameter, eg, tree trunks, fruits (v) Increase in fresh or dry weight. One single maize root apical meristem can given to more than 17,500 new cells per hour, wheres as cell in watermelon may increase in size by upto 3, 50,000 the former, growth is expressed as increase the cell number latter expresses growth as increase in the size of cell.

Photophosphorylation is the conversion of ADP to ATP using the energy of sunlight by activation of PSII. This involves the splitting of the water molecule in oxygen and hydrogen protons (H⁺), a process known as photolysis.

Photosynthesis takes place only in the green parts of the plants, mainly the leaves.