Plant responses

Question 1

What is abscission?

Answer 1

A process where a plant sheds parts, particularly leaves, fruit and seeds when their loss is beneficial to the plant.

Question 2

What is an autotroph?

Answer 2

An organism that is able to produce complex organic molecules from molecules found in its environment, using an external energy source.

Question 3

What is critical day length?

Answer 3

A period of day length that when exceeded triggers flowering in long-day plants or inhibits flowering in short-day plants

Question 4

What is ethylene?

Answer 4

A plant hormone that promotes the ripening of fruit

Question 5

What is gravitropism?

Answer 5

Growth towards or away from a gravitational attraction

Question 6

What is hydrotropism?

Answer 6

Growth towards or away from water

Question 7

What is a long-day plant?

Answer 7

A plant that is triggered into flowering when nights become shorter than a critical day length. Early summer and late spring.

Question 8

What is a nastic response?

Answer 8

A nastic response is a fast and reversible turgor movement. They rely on changes in turgor pressure within certain plant cells.

Question 9

What is nyctinasty?

Answer 9

A circadian rhythmic movement of plants in response to the onset of darkness

Question 10

What is photoperiod?

Answer 10

The period of time each day which an organism receives sunlight.

Question 11

What is photosynthesis?

Answer 11

The process by which plants and some bacteria use the energy from sunlight to produce glucose from carbon dioxide and water.

Question 12

What is photoperiodism?

Answer 12

The response of an organism to seasonal changes in the photoperiod.

Question 12

What is phototropism?

Answer 12

Growth towards or away from a source of light

Question 13

What is a thigmotropism?

Answer 13

A thigmotropism is movement in which a plant moves or grows in response to touch or contact stimulu. Commonly seen in climbing plants with coil-like structures called tendrils.

Question 13

What is phytohormone?

Answer 13

Any of a range of chemicals that regulate plant growth

Question 13

What is phytochrome?

Answer 13

A blue-green pigment found in many plants that regulate various developmental processes, particularly flowering

Question 14

What is a thigmonastic response?

Answer 14

A nastic response triggered by touch.

Question 14

What is a short-day plant?

Answer 14

A plant that is triggered into flowering when nights become longer than a critical length. Autumn/Winter.

Question 14

How does the ability of stems and leaves to change their orientation towards a moving light source give plants an adaptive advantage?

Answer 14

Able to receive maximum light intensity to optimise the rate of photosynthesis.

Question 14

What is a tropism?

Answer 14

A tropism is a long term, slow growth movement toward or away from a stimulus. They result in permanent changes in the size of some cells.

Question 14

How does the ability to time flowering with other members of the species give plants an adaptive advantage?

Answer 14

Synchronous flowering increases chance of cross fertilisation and reduces wastage of gametes and nectar. It may also allow plant to synchronise with its pollinator.

Question 15

How is the ability to change the direction of root growth toward a source of water an adaptive advantage for plants?

Answer 15

Maintain photosynthesis and turgor pressure despite changes in location of water supply.

Question 15

How does the ability of stems and leaves to grow upwards towards sunlight give plants an adaptive advantage?

Answer 15

The plant is able to compete successfully with other plants for sunlight and avoid over-shading.

Question 15

How does the ability to grow roots in a downward direction give plants an adaptive advantage?

Answer 15

Access to water for photosynthesis

Question 16

What is primary plant growth?

Answer 16

Growth by cell division and elongation and the early stages of differentiation before tissues become woody (lignified).

Question 17

How do Auxins effect phototropism?

Answer 17

The higher concentration of auxin on the shaded side of the plant causes greater elongation.

Question 18

What is an auxin?

Answer 18

A plant hormone that causes cell enlongation in the root and shoot tip and controls some plant growth processes.

Question 19

Roots and shoots - gravitropism:

Answer 19

The root grows downwards because the plant can detect gravity. Therefore, they exhibit a positive gravitropism.

Shoots grow upwards. Negative gravitropism.

Question 20

Auxins and thigmotropism:

Answer 20

Cells on the side of the plant touching the object produce auxin and transport it to the cells on the opposite side of the tendril. High concentrations of auxin in these ‘untouched’ cells stimulates elongation and faster growth rates, resulting in the tendrils bending around the object.

Question 21

What are some nastic responses?

Answer 21

Nyctinasty - movements at night or in the dark
Photonasty - response to light
Thigmonasty - response to touch

Question 22

What is nyctinasty?

Answer 22

A circadian-rhythm based nastic movements of plants in response to darkness, or a plant “sleeping”.

For example, the leaves of a plant drooping.

Question 23

What is Pr and Pfr?

Answer 23

The mechanism that plants use to measure photoperiod involves the light-sensitive protein phytochrome.

When Pr absorbs light, it is converted to Pfr. Sunlight contains more red light than far-red light, so Pfr predominates during the day. When Pfr absorbs far-red light it is rapidly converted back into Pr. During darkness, there is a slow conversion of Pfr back to Pr.

Therefore, phytochrome controls flowering as during the night the slow conversion of Pfr to Pr acts as a clock.

Pfr levels are highest in plants at the peak of summer, when day length is greatest.