22) Plant reproduction

Question 1

Define daily heat unit

Answer 1

the amount of heat a plant experiences in a day

Question 2

What is the growth and development of a plant usually dependent on and why?

Answer 2

temperature

a set number of daily heat units are required between developmental stages

Question 3

Define vernalisation

Answer 3

an extended period of exposure to low temperatures that stimulates flowering

Question 4

What does vernalisation promote?

Answer 4

transcription of genes associated with flowering

Question 5

What can plants measure to ensure they only flower when it is favourable to do so?

Answer 5

changes in the length of night and day

Question 6

Describe long-day plants

Answer 6

flower during late spring when day length rises above a critical value

Question 7

Describe short-day plants

Answer 7

flower as nights grow longer and day length drops below a critical value (but length of dark period is more important)

Question 8

Define phytochrome

Answer 8

photoreceptor (light-sensitive protein) that enables plants to measure changes in day length

Question 9

The conversion between two isomers enables plants to measure day length. Name these two isomers

Answer 9

Pr and Pfr

Question 10

Describe the conversion between Pr and Pfr

Answer 10

Pr absorbs red light (660nm) -> Pfr

Pfr accumulates during the day, absorbs far red light (780nm) -> Pr at night

Question 11

What do the relative proportions of Pr and Pfr dictate?

Answer 11

flowering time

Question 12

Name the 7 key parts of a flower

Answer 12

stigma
style
anther
petal
filament
sepal
ovary

Question 13

Where are the male gametes found in a plant?

Answer 13

within pollen grains

Question 14

Where are the female gametes found in a plant?

Answer 14

in ovules

Question 15

What must happen for a plant to reproduce?

Answer 15

pollen from the anthers on one plant must be transferred to the stigma of another plant

Question 16

State 2 adaptations of insect-pollinated flowers

Answer 16

nectar

colourful + fragrant - attract pollinators

Question 17

State 3 adaptations of wind-pollinated flowers

Answer 17

light pollen grains - carried easily by wind
many pollen grains produced
anthers + stigma with a large surface area hand outside the flower exposed to air currents

Question 18

Name the 3 parts of an endospermic seed

Answer 18

embryo - formed by successful fertilisation
endosperm - food source surrounding the embryo (primarily starch)
seed coat - testa, protective outer layer

Question 19

Some seeds lack an endosperm, what do they use as a food source?

Answer 19

cotyledons (seed leaves) which during the development of the seeds absorb food reserves from the endosperm

Question 20

Describe the 4 steps of fertilisation and seed formation

Answer 20

1. pollen grain lands on the stigma of another plant
2. pollen tube grows from the grain towards the ovule
3. double fertilisation: pollen tube delivers two sperm cells to the ovary at the same time
   - one fertilises an egg cell forming an embryo
   - nucleus of the other fuses with the two polar nuclei at the centre of the embryo sac forming the endosperm
4. the ovules develop into seeds and the surrounding ovary into a fruit

Question 21

Define seed germination

Answer 21

the process by which a plant grows from a seed

Question 22

Describe what happens at the beginning of germination

Answer 22

after a seed has been exposed to water, starch in the endosperm is hydrolysed to glucose
gibberellins initiate the breakdown of starch by inducing the synthesis of amylase

Question 23

Define gibberellins

Answer 23

plant hormones which act as cell signalling molecules

Question 24

What is seed germination dependent on?

Answer 24

internal and external environmental conditions which differ between species e.g. temperature, water, oxygen, and light levels

Question 25

How are cereals a staple food?

Answer 25

the endosperm within a seed can act as a source of nutrition / carbohydrate

Question 26

Suggest the implications of the increasing use of cereal crops e.g. wheat, maize and rice

Answer 26

global consumption may exceed production (remaining stock is utilised from previous years)
as the world’s population increases, food demand increases however, less land is available, water is limited and fertilisers and fuel costs increase