3.6.1.1 Survival and response

What is the primary role of specific growth factors in flowering plants?

• To provide nutrients to the plant

• To regulate growth in response to directional stimuli

• To protect the plant from pests

• To increase the plant's water absorption

Answer explanation

Specific growth factors primarily regulate growth in response to directional stimuli, guiding processes like phototropism and gravitropism, rather than providing nutrients, protecting from pests, or increasing water absorption.

Which plant hormone is primarily involved in cell elongation in response to gravitropism and phototropism?

• Gibberellin

• Cytokinin

• Indoleacetic acid (IAA)

• Ethylene

Answer explanation

Indoleacetic acid (IAA) is the primary plant hormone responsible for cell elongation, particularly in response to gravitropism and phototropism, facilitating growth towards light and gravity.

How does indoleacetic acid (IAA) affect cell elongation in the shoots of flowering plants?

• It inhibits cell elongation

• It promotes cell elongation

• It has no effect on cell elongation

• It causes cell death

Answer explanation

Indoleacetic acid (IAA) is a plant hormone that promotes cell elongation in the shoots of flowering plants by stimulating cell division and growth, leading to increased length and overall growth of the plant.

What is the effect of high concentrations of indoleacetic acid (IAA) on root growth?

• It promotes root growth

• It inhibits root growth

• It has no effect on root growth

• It causes root cells to die

Answer explanation

High concentrations of indoleacetic acid (IAA) can inhibit root growth by disrupting normal cell elongation and division processes, leading to reduced root development.

What is gravitropism?

• Growth response to light

• Growth response to gravity

• Growth response to water

• Growth response to temperature

Answer explanation

Gravitropism is the growth response of plants to gravity, where roots grow downward and stems grow upward. This distinguishes it from other tropisms like phototropism, which is a response to light.

What is phototropism?

• Growth response to light

• Growth response to gravity

• Growth response to water

• Growth response to temperature

Answer explanation

Phototropism is the growth response of plants towards light. This phenomenon allows plants to maximize their exposure to sunlight, which is essential for photosynthesis, making 'growth response to light' the correct choice.

What is the primary purpose of taxes in mobile organisms?

• To find food

• To maintain a favourable environment

• To reproduce

• To communicate with other organisms

Answer explanation

The primary purpose of taxes in mobile organisms is to maintain a favourable environment, which is essential for their survival and functioning. This ensures they can thrive and carry out necessary life processes.

What is a kinesis?

• A directional movement in response to a stimulus

• A non-directional movement in response to a stimulus

• A growth response to light

• A growth response to gravity

Answer explanation

Kinesis refers to a non-directional movement in response to a stimulus, unlike taxis, which is directional. This means that the movement does not have a specific orientation towards or away from the stimulus.

Which of the following is an example of a simple reflex?

• A plant bending towards light

• A human pulling their hand away from a hot surface

• A bird building a nest

• A fish swimming upstream

Answer explanation

A human pulling their hand away from a hot surface is a simple reflex, as it is an automatic response to a stimulus (heat) that does not involve conscious thought, unlike the other options which involve more complex behaviors.

How many neurons are involved in a three-neurone simple reflex arc?

• One

• Two

• Three

• Four

Answer explanation

A three-neurone simple reflex arc consists of three types of neurons: a sensory neuron, an interneuron, and a motor neuron. Therefore, the correct answer is three.