Test: Biology Minor Mock Test- 3 (March 21) - NEET MCQ

Please note that there are 2 sets of information given in the question. The first set (options a-e) mentions the names of compounds. The second set (options 1-4) mentions the combinations of the first set of options.

• Auxin refers to a group of plant hormones that regulate plant growth.
• Based on their origin, auxins can be divided into:
  • Natural Auxins - They occur naturally in the plant and affect physiological functions. E.g. - IAA, IBA.
  • Artificial Auxins - These are synthetically-derived chemical compounds that resemble IAA in biological activity. E.g. - NAA.
• Artificial auxins are widely used in horticultural practices, as weedicides, rooting agents, and defoliating agents.

• IPA
  • Indole-3-pyruvic acid (IPA) is an intermediate in the IAA biosynthesis pathway.
  • Hence, it is not an artificial auxin.
• PAA
  • Phenylacetic acid (PAA) is a natural auxin.
• NAA
  • Naphthalene acetic acid (NAA) is an artificial auxin that is used as a rooting agent.
• 2,4,5-T
  • 2,4,5 - Trochlorophenoxyacetic acid is an artificial auxin that is used as a herbicide.
• 2,4-D
  • 2,4 - Dichlorophenoxy acetic acid (2,4-D) is an artificial auxin that is widely used as a herbicide.

Thus the answer will be (c), (d), and (e).

Solution: Gibberellins are involved in various growth processes including overcoming seed dormancy, promoting flowering, and enhancing fruit size. However, inducing root hair formation is a function attributed to ethylene, not gibberellins. Gibberellins are particularly known for their role in promoting stem elongation and seed germination

• Gibberellic acid is a Terpene.
• All known gibberellins are diterpenoid acids that are synthesized by the terpenoid pathway in plastids and then modified in the endoplasmic reticulum and cytosol until they reach their biologically-active form.
• All gibberellins are derived via the ent-gibberellane skeleton, but are synthesized via ent-kaurene.

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.

The plant hormone auxin is used for agriculture and horticulture.

• During the process of plant propagation, auxin is used to initiate rooting in stem cutting.
• Auxin performs the role of promoting flowering in the plant.
• Abscission of older mature fruits and leaves is regulated by the hormone auxin.
• It also prevents leaves and fruits from dropping at the early stage. The growing apical buds in most higher plants inhibit the growth of auxiliary buds. This phenomenon is called apical dominance.

Therefore, the correct answer is option D.

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.

Auxins are generally produced by the growing apices of the stems and roots, from where they migrate to the regions of their action. In most higher plants, the growing apical bud inhibits the growth of the lateral (axillary) buds, a phenomenon called apical dominance.

The apical bud produces an auxin hormone that inhibits the growth of the lateral buds further down on the stem towards the axillary bud.

The term auxin has been derived from the Greek word “auxein” which means “to grow”. It is known to be the first plant hormone that was discovered.

• Auxins are a group of compounds that include indole-3-acetic acid (IAA), and other natural and synthetic compounds that have certain growth-regulating properties. They are one of the various plant growth regulators(PGRs). They are generally produced by the growing apices of the stems and roots; from where they migrate to the other regions of their action. Auxins can be natural or synthetic. Indole Acetic Acid(IAA) and indole butyric acid (IBA) are some natural auxins that have been isolated from plants.
• Some synthetic auxins include NAA (naphthalene acetic acid) and 2, 4-D (2, 4-dichlorophenoxyacetic) which are used for various purposes.

Functions:

• Physiological:
  • Cell Elongation: Auxin promotes elongation and growth of stems and roots and enlargement of fruits by overall enlargement of cells in all directions,
  • Apical Dominance: In many plants, the apical bud grows while the lower axillary buds are suppressed. This is an effect of the auxin(IAA) of the axillary bud. This can be proven but removing the apical bud which then results in the growth of lateral buds.
  • Control abscission layer: Auxin inhibits the abscission of young leaves and fruits in normal amounts. An abscission layer is produced only when the auxin content is reduced below the minimum level which ultimately leads to the fall of ripe fruits.

There are many other uses:

• Rooting: Auxin stimulates root formation in woody stem cuttings.
• Flowering: The dilute solutions of synthetic auxins are sprayed on fruits like litchi and pineapple which induce flowering in them. However, in most plants, flowering will be inhibited by spraying a high concentration of auxins.
• Parthenocarpy: Auxins in diluted form can be used to produce parthenocarpic or seedless fruits. It has been proven that naturally parthenocarpic fruits like bananas and grapes have higher internal production of auxins.
• Weedicides: Spraying synthetic auxins like 2,4-D is a procedure commonly used as weedicides. They are used to remove many broad-leaved weeds or dicotyledonous weeds while sparing the monocot plants.
• Except for auxin, there are four other plant hormones called gibberellins, cytokinin, abscisic acid, and ethylene. Together they are called Plant Growth Regulators (PGRs). Some of them cause the plants to grow, while others like abscisic acid promote senescence. i.e. promote falling of leaves and fruits. Ethylene is the only gaseous hormone.

Expiration muscles come into action when you force expiration. The expiratory muscles are the abdominal muscles and intercostals. It is rare if a patient is contracting abdominal muscles for quiet breathing and he is trying to force expiration.

• Alveoli is a thin, irregular walled and vascularized bag-like structure.
• It is the main site for diffusion of gases.
• Terminal bronchioles give rise to alveoli.
• Lungs without alveoli is a dead lung as they play a major role in respiration.

Mucus helps to moisten and protect the airways. Mucus lines the ciliated cells of the trachea to trap inhaled foreign particles that the cilia then waft upward toward the larynx and then the pharynx where it can be either swallowed into the stomach or expelled as phlegm.

'Motile' (or moving) cilia are found in the lungs, respiratory tract and middle ear. These cilia have a rhythmic waving or beating motion. They work, for instance, to keep the airways clear of mucus and dirt, allowing us to breathe easily and without irritation. They also help propel sperm.

Chloride shift also known as the Hamburger phenomenon is a process which occurs in a cardiovascular system and refers to the exchange of bicarbonate (HCO₃⁻) and chloride (Cl⁻) across the membrane of red blood cells (RBCs).

Oxygen haemoglobin dissociation curve gives the relationship between the saturation of haemoglobin and oxygen tension.
The curve obtained by plotting percent saturation of Hb against time is sigmoid, at 30°C and pH7.4. Dissociation of oxyhaemoglobin can be promoted by rise in the body temperature and low pH (high CO₂).

The oxygen-carrying capacity of hemoglobin determines how much oxygen is carried in the blood.

In addition, other environmental factors and diseases can also affect oxygen-carrying capacity and delivery; the same is true for carbon dioxide levels, blood pH, and body temperature.

When carbon dioxide is in the blood, it reacts with water to form bicarbonate (HCO^{3 −}) and hydrogen ions (H⁺). As the level of carbon dioxide in the blood increases, more H+ is produced and the pH decreases.

The increase in carbon dioxide and subsequent decrease in pH reduce the affinity of hemoglobin for oxygen. The oxygen dissociates from the Hb molecule, shifting the oxygen dissociation curve to the right.

Therefore, more oxygen is needed to reach the same hemoglobin saturation level as when the pH was higher.

• Bronchi, bronchioles, and alveoli together comprise the lung.
• They are the main vital organs compared to other secondary parts.
• They have a perfect network for respiration to take place.

• The nodal musculature has the ability to generate action potentials without any external stimuli.
• The number of action potentials that could be generated in a minute varies at different parts of the nodal system.
• The SAN can generate the maximum number of action potentials and is responsible for initiating and maintaining the rhythmic contractile activity of the heart.
• Therefore, it is called the pacemaker.

• Platelets, also called thrombocytes, are cell fragments produced from megakaryocytes.
• Platelets can release a variety of substances most of which are involved in the coagulation or clotting of blood.

The hepatic portal vein carries blood from the intestine to the liver before it is delivered to the systemic circulation.

Prehypertension is defined as a systolic pressure from 120–139 millimeters of mercury (mm Hg) or a diastolic pressure from 80–89 mm Hg.

Through this streak, cells migrate from the upper layer by the process called gastrulation to form the three germ layers of the embryo proper: the ectoderm, the endoderm, and the mesoderm.The cells that are destined to form the heart are also derived from this mesodermal layer.

The cardiovascular centre is a part of the human brain responsible for the regulation of the rate at which the heart beats through the nervous and endocrine systems. It is found in the medulla oblongata.

(a) When circulating in the bloodstream and inactivated, neutrophils are spherical.
Once activated, they change shape and become more amorphous or amoeba-like and can extend pseudopods as they hunt for antigens.

(b) Eosinophil cells are 12 - 17 µm in diameter - larger than neutrophils, and about 3 times the size of a red blood cell. You can see that eosinophils only have two lobes to their nucleus.

(c) In blood, basophils are round, but the shape changes as they migrate into tissues. They generally have a multilobed nucleus and no evidence of nucleoli.
Basophils also have an abundance of condensed chromatin around the periphery of the nucleus.

(d) Monocytes are the largest type of white blood cells and can be up to 20µm in diameter.
They have a large eccentrically placed nucleus, which is kidney bean-shaped. They have abundant cytoplasm and some fine pink/purple granules in the cytoplasm.

(e) Lymphocytes can look like monocytes, except that lymphocytes do not have a kidney-bean shaped nucleus, and lymphocytes are usually smaller.
They have a small spherical nucleus and have abundant dark staining condensed chromatin. Not much cytoplasm can be seen, and it is basophilic (pale blue/purple staining).

The pericardium is the protective covering of the heart. The pericardium is made of different layers to perform different functions.
The layer of heart pericardium which checks its overstretching and overfilling as well as protects the heart from mechanical injury is fibrous pericardium.

The glomerulus is a tuft of capillaries

• Blood enters the glomerulus through the afferent arteriole, a fine branch of the renal artery.
• Blood from the glomerulus is carried away by an efferent arteriole.

Detailed Explanation:

Option A is wrong because blood enters through the afferent arteriole and not the efferent. 

Option B is wrong because there is no such radial arteriole present. And, The collecting duct system is the last part of the nephron and participates in electrolyte and fluid balance through reabsorption and excretion, processes regulated by the hormones aldosterone and vasopressin (antidiuretic hormone). 

Option C is wrong because blood doesn't enter through distributing arteriole because no such arteriole is present. 

Option D is right because blood enters glomerular capillaries through the afferent arteriole and leaves through the efferent arteriole. 

Hence Option D is correct. 

Uric acid is  less toxic than ammonia or urea. It contains four nitrogen atoms; only a small amount of water is needed for its excretion. Out of solute, it precipitates and forms crystals.

Detailed Explanation:

Option A is wrong because Urea moves to the blood and gets filtered and eliminated with water in urine via the kidneys.

Option B is correct Uric acid is insoluble in water as there are in solid form, thus, containing the least water.
In birds, uric acid mixes with undigested food to form the bird dropping.

Option C is wrong because Ammonia is very toxic and needs water for diffusion.

Option D is wrong because none of the above options has the same toxicity level. 

Hence Option B is correct.

During micturition, parasympathetic stimulation causes the detrusor muscle to contract and the internal urethral sphincter to relax. The external urethral sphincter (sphincter urethrae) is under somatic control and is consciously relaxed during micturition. 

Detailed Solution:

Option A is right because, during micturition, parasympathetic stimulation causes the detrusor muscle to contract and the internal urethral sphincter to relax.

Option B is wrong because the muscles of the urinary bladder contract and do not relax. 

Option C is wrong because during micturition, the muscles don't show fatigue. 

Hence, the correctb option is A. 

Renal corpuscle, also called malpighian body, filtration unit of vertebrate nephrons, functional units of the kidney.
It consists of a knot of capillaries (glomerulus) surrounded by a double-walled capsule (Bowman’s capsule) that opens into a tubule.