Tag: biology

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Questions Related to biology

Multiple choice apical dominance auxins and gibberellins growth and development plant growth and development biology

The discovery, that during light induced bending of stem the apex produces a diffusible chemical, was made by

  1. Charles Darwin and Francis Darwin

  2. Boysen-Jensen and Paal

  3. Went

  4. Van Overbeek
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

A tropism is a growth movement by plant part in the direction of the stimulus. According to Boysen-Jensen, the stimulus for phototropism, growth in response to light, is a diffusible chemical that passes from the tip of the coleoptile. He cut the tip of the coleoptile and the severed tip was reattached through a gelatin disc. The recapitated coleoptile showed bending of stem towards light. Paal continued with Boyse-Jensen work. He said that the tip of coleoptile produces some chemical which travels down and stimulates growth. The light causes the accumulation of that chemical on the shaded side of the coleoptile. 

Thus, the correct answer is option B. 

Multiple choice apical dominance auxins and gibberellins growth and development plant growth and development biology

Decapitation i.e. removal of shoot tips in a plant usually results in

  1. inactivation of lateral buds

  2. growth of lateral buds

  3. cessation of plant growth

  4. yellowing of leaves.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation
Apical dominance is the phenomenon by which presence of apical bud does not allow the nearby lateral buds to grow. When the apical bud is removed, the lateral buds sprout. Apical bud inhibits the growth of lateral buds by releasing auxins. When a plant is decapitated i.e., its apical bud is removed then the lateral buds sprout, resulting in dense bushy growth. This phenomenon is widely used in the tea plucking and hedge making.
So the correct answer is 'growth of lateral buds'.
Multiple choice apical dominance auxins and gibberellins growth and development plant growth and development biology

Growth hormone responsible for apical dominance is

  1. Auxin

  2. Cytokinin

  3. Gibberellin

  4. Ethylene
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Apical dominance is a phenomenon in which central stem is dominant and lateral stems are suppressed. It is due to plant hormones produced in the tip of the shoot. Auxin hormone is responsible for apical dominance and cytokinin hormone is responsible for breaking the apical dominance. 

Thus, the correct answer is option A.

Multiple choice apical dominance auxins and gibberellins growth and development plant growth and development biology

Substances which originate at the tip of stem and control growth elsewhere are

  1. Enzymes

  2. Hormones

  3. Vitamins

  4. None of the above
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

A chemical substance produced in one part of body and regulates the activity of other parts is called as hormones. Plant hormones are produced in the stem, bud and root tips and control the plant growth, formation of flowers, stems, leaves, development, and ripening of fruit, etc. Auxins are specialized hormones which acts on the tip.

Thus, the correct answer is option B.

Multiple choice apical dominance auxins and gibberellins growth and development plant growth and development biology

Apical dominance means

  1. Suppression of growth of apical bud by axillary buds

  2. Suppression of growth of axillary buds by the presence of apical buds

  3. Stimulation of growth of axillary buds by removal of apical buds

  4. Inhibition of growth of axillary buds by removal of apical buds
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

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 as apical dominance. 

Apical dominance is thought to be due to production of auxins in the stem tips. Removal of shoot tips (decapitation) usually results in the growth of lateral buds. It is widely applied in tea plantations, hedge-making.

Multiple choice biology nervous system the reflex action reflex action and reflex arc basic reflex action and reflex arc

Reflex arc is formed by 

  1. Receptor - brain - muscles

  2. Muscles - spinal cord - receptor

  3. Receptor - spinal cord - muscles

  4. Muscle - brain - receptor
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The reflex arc is a simple nervous pathway and consists of the sensory receptor, afferent neuron, centre, efferent neuron and effector organ. The afferent/sensory neurons transmit the sensory information from sensory receptors to the spinal cord (sensory pathway). Reflex arc starts with sensory receptors, not with muscles. The interneurons of spinal cord integrate the incoming information and signal is relayed to motor/efferent neurons.  The motor pathway transmits the signal from motor neurons to the effector organs (muscles and glands etc). Thus, reflex arc transmits the information from receptor to effector via the spinal cord which. The brain is not the part of reflex arc. Thus, the correct answer is option C.

Multiple choice biology nervous system the reflex action reflex action and reflex arc basic reflex action and reflex arc

The sequence of a reflex arc is

  1. Receptor $\rightarrow$ Sensory neuron $\rightarrow$ Motor neuron $\rightarrow$ Effector $\rightarrow$ Response
  2. Effector $\rightarrow$ Sensory neuron $\rightarrow$ Motor neuron $\rightarrow$ Receptor $\rightarrow$ Response
  3. Effector $\rightarrow$ Motor Neuron $\rightarrow$ Interneuron $\rightarrow$ Receptor $\rightarrow$ Response
  4. Receptor $\rightarrow$ Motor neuron $\rightarrow$ Sensory neuron $\rightarrow$ Effector $\rightarrow$ Response
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Reflex arc transmits the sensory information from receptor to effector via spinal cord. It consists of sensory receptor, afferent (sensory) neuron, centre, efferent (motor) neuron and effector organ. The afferent/sensory neurons transmit the sensory information from sensory receptors to spinal cord (sensory pathway). Detection of environmental stimulus by receptors forms the first step of reflex arc. 

Sensory neurons receive the information from receptors while motor neurons transmit the nerve impulses from CNS to effectors (muscles and glands). 
The interneurons of spinal cord integrate the incoming information and signal is relayed to motor/efferent neurons.  The motor pathway transmits the signal from motor neurons to the effector organs (muscles and glands etc). The effector organs respond according to the information carried by motor pathway.
Therefore, the correct answer is option A.

Multiple choice biology nervous system the reflex action reflex action and reflex arc basic reflex action and reflex arc

All are examples of cranial reflexes but not

  1. Salivation

  2. Scratching

  3. Blushing

  4. Sneezing
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Reflex arc consists of sensory receptor, afferent neuron, centre, efferent neuron and effector organ. The reflexes that involve sensory and motor nerve fibres of cranial nerves and control the head region are known as cranial reflexes. Since, cranial reflexes involve head, eyes, nose, mouth, swallowing and facial expression, they produce the vital and involuntary responses. Spinal reflexes are the one in which spinal cord serves as centre without involvement of brain. They control the voluntary responses of other body parts via spinal cord. Salivation in response to sight/smell/thought of food, blushing and sneezing are involuntary actions, which involve mouth, facial expression and nose, and thus are categorized under cranial reflexes. Scratching is a voluntary response to itch stimulus in which brain is not involved and thus is a spinal reflex. 

Therefore, the correct answer is option B.

Multiple choice biology nervous system the reflex action reflex action and reflex arc basic reflex action and reflex arc

The reflex arcs in which one or more interneurons connect the afferent and efferent signals are

  1. Autonomic reflex

  2. Somatic reflex

  3. Monosynaptic reflex

  4. Polysynaptic reflex
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

  • Monosynaptic reflex is a type of reflex in which the reflex arc consists of only two neurons, one sensory neuron, and one motor neuron. Monosynaptic refers to the presence of a single chemical synapse. 
  • By contrast, in polysynaptic reflex arcs, more than one relay neurons connect the sensory and motor neuron. 
  • Polysynaptic reflex or spinal reflex or withdrawal reflex protects the body from the damaging stimulus. It is located in the spinal cord. 

Therefore, the correct answer is option D.