Seeds and Germination

Question 1

What is a seed?

Answer 1

The result of sexual reproduction,
A new generation with characteristics of both parents,
A survival mechanism.

Question 2

Name 8 components of seed structure.

Answer 2

Testa,
Hilum,
Plumule,
Epicotyl,
Hypocotyl,
Embryo,
Radicle,
Cotyledon.

Question 3

What is a testa?

Answer 3

The covering layer of the seed.

Question 4

What is a cotyledon?

Answer 4

Fleshy lobes that act as a starch/ nutrient store for germination.

Question 5

What is an embryo?

Answer 5

The embryo contains genetic information from both parents.

Question 6

What is a plumule?

Answer 6

The embryonic shoot.

Question 7

What is a radicle?

Answer 7

The embryonic root.

Question 8

What is the epicotyl?

Answer 8

The shoot from which the entire plant shoot system developed. The growing tip of the epicotyl is the plumule.

Question 9

What is the hypocotyl?

Answer 9

The zone between the rudimentary root and shoot.

Question 10

Define dormancy.

Answer 10

A state of metabolic arrest that facilitates the survival of organisms during environmental conditions that are incompatible with their regular course of life.

or

Temporary failure of a viable seed to germinate in conditions that favour germination.

Question 11

Describe enforced dormancy.

Answer 11

Dormancy is forced upon the seed by some limitation of the germination environment.

Question 12

Describe innate dormancy.

Answer 12

Dormancy is imposed upon the seed by the mother plant. The seed remains dormant for some time after the seed is shed, even under perfect conditions.

Question 13

Describe induced/ secondary dormancy.

Answer 13

Acquired condition of the inability to germinate caused by some experience after ripening.

Question 14

State 3 ways pyroendemics break dormancy.

Answer 14

Fracturing or desiccation of the seedcoat by heat.
Heat signals may directly stimulate the embryo.
Chemicals from combustion induce germination.

Question 15

Name 3 seed treatments.

Answer 15

Seed priming,
Seed coating,
Seed conditioning.

Question 16

Describe germination (4 points).

Answer 16

The transition from embryonic to post-embryonic growth.
Starts with imbibing the seed in water, causing swelling and an increase in size.
Cells elongate and being to divide and differentiate.
Leaves begin to photosynthesise and the new plant becomes independent of energy stored in the seed.

Question 17

How do gibberellin and abscisic acid affect germination?

Answer 17

Gibberellin stimulates, ABA represses.

Question 18

State 3 points related to temperature and germination.

Answer 18

Seeds continuously deteriorate and will die unless they germinate.
Most seeds are initially dormant, relatively dry seeds continuously lose dormancy at a rate that is temperature dependent.
Once seeds lose dormancy the rate of germination increases linearly between the base and optimum temps. and declines linearly between optimum and ceiling temps.

Question 19

Describe light-mediated seed germination.

Answer 19

It is a mechanism for avoiding germination in the shade of other plants. Generally favoured by sun-loving seed plants like Arabidopsis, that lack the energy reserves to emerge and then elongate out from beneath the shade of other plants.

Question 20

Describe light-dependent seed germination.

Answer 20

Seed germination is suppressed in the dark and stimulated in sunlight.
An adult leaf will filter out the red light required for germination, but not far-red light which inhibits germination.
When no adult canopy is present, red light stimulates germination.

Question 21

What kind of seeds tend to be able to germinate in the dark?

Answer 21

Large seeds.

Question 22

Describe a recalcitrant seed.

Answer 22

Short-lived seeds that can not be dried to below 20-30% moisture content without injury, and won’t tolerate freezing.

Question 23

Describe an orthodox seed.

Answer 23

A long-lived seed that can be frozen and dried to 5% moisture content.

Question 24

What is vigour in seed terms?

Answer 24

A measure of quality.

Question 25

What is a high vigour seed?

Answer 25

A quick and uniformly germinating seed.

Question 26

What is a low vigour seed?

Answer 26

A slow and erratically germinating seed.

Question 27

What is seed viability?

Answer 27

A seeds possession of the requirements to germinate.

Question 28

What is seed longevity?

Answer 28

Life span or the length of time they remain viable. Dependant on species and storage environment.