Seeds

Question 1

What is meant by the term seed?

Answer 1

A seed is the product of sexual reproduction. A seed is a fertile & ripened ovule that contains an embryonic plant, usually supplied with stored food and surrounded by a protective coat called a testa.

Question 2

Identify the benefits to the plant of sexual reproduction

Answer 2

Sexual reproduction involves the mixing of the genetic material of 2 different individuals and thus generates diversity.
Genetic diversity is important, it increases the possibility of survival of at least some of a species where the environment is subject to change.
It also creates the possibility the possibility of new combinations of genetic info that may make a species more successful.

Question 3

Describe the internal structure of dicot seed and eg.

Answer 3

Dicot seed Phaseolus vulgaris.
Testa
Cotyledon
Embryo 
Radicle 
Plumule 
Hypocotyl
Epicotyl 
Hillmorton
Micropyle

Question 4

Horticultural benefits of propagating from seed (5)

Answer 4

1. Easily stored
2. Avoid virus transmission
3. Only way for some species
4. May get large no. from each plant
5. Produces variation and potential for new cultivars

Question 5

Testa

Answer 5

Seed coat that protects the seed, can be very tough, may need to be damaged to allow seed germinate

Question 6

Hilum

Answer 6

The point where the seed is attached to the fruit

Question 7

Micropyle

Answer 7

Small hole in testa where the pollen tube entered, can be the point where water enters seed to start germination process.

Question 8

Embryo

Answer 8

made up of
Cotyledons 
Plumule 
Epicotyl 
Hypocotyl 
Radicle

Question 9

Radicle

Answer 9

Part of seed that will form first root

Question 10

Cotyledon

Answer 10

Seed leaf - store of food

Question 11

Plumule

Answer 11

Part of seed that will form the first shoot

Question 12

Hypocotyl

Answer 12

Connects the Plumule & radicle

Question 13

Limitations of plant propagation from seed (5)

Answer 13

1. Some plants may not produce viable seed
2. Difficult germination
3. Lack of uniformity
4. Time to maturity
5. Some seeds do not store easily

Question 14

Examples of plants usually propagated from seed (5)

Answer 14

1. Phaseolus vulgaris
2. Daucus carota
3. Lobelia erinus
4. Nigella damascena
5. Lolium perenne

Question 15

State the main horticultural uses of seed

Answer 15

Vegetable & bedding production
Annuals
Lawns

Question 16

State what is meant be seed viability

Answer 16

Seeds contain a living embryo and will germinate when conditions are right

Question 17

List requirements for seed germination (4)

Answer 17

1. Moisture - moisture levels need to be restored to about 70%. Moisture is absorbed through the testa by imbibition. This softens the testa & cell walls. plant cells take up water by osmosis
2. Temperature - Temp very important and usually specific to species. Respiration was not happen if temp not correct. Temp may July need to be 4°C or could be 30°C. Also critical max above which won’t germinate
3. Oxygen - Aerobic Respiration requires oxygen to be present, allowing the plant embryo to develop. Anaerobic germination takes place if there is an absence of oxygen leading to death of seed or suspended germination called induced dormancy.
4. Light/dark - Most species are indifferent to the influence of light for germination but some are sensitive. Some require while some inhibited by it.

Question 18

State meaning of seed dormancy

Answer 18

Not all seeds are able to germinate when supplied with water and maintained at temperatures favourable to growth. Such seeds are said to be dormant. Conditions needed to break dormancy usually relate to the natural environment and conference a selection Tiverton advantage to the species.

Question 19

3 types of dormancy

Answer 19

1. Innate dormancy - Most seeds have a period of innate dormancy. Begins immediately when embryo ceases to grow and still attached to parent plant.
2. Induced dormancy -
3. Enforced dormancy - capable of germination but prevented by immediate environmental conditions
   Some seeds are born dormant, some achieve it and some have it thrust upon them.

Question 20

Osmosis

Answer 20

Osmosis is the process by which water moves across a semi-permeable membrane, from a solution with a lower salt concentration to a solution of higher salt concentration.

Question 21

Endosperm

Answer 21

Formed at fertilisation, used as a source of food for the embryo as it grows within the seed

Question 22

Tropism

Answer 22

The direction in which a part of a plant grows, according to some external stimulus is called a tropism.

Question 23

Geotropism

Answer 23

The root always grows downwards irrespective of its position in the soil. This is because of the roots response to gravity known as geotropism.

Question 24

Phototropism

Answer 24

The Hypocotyl will automatically grow up towards the light because of the response to light called phototropism

Question 25

Germination - how it occurs

Answer 25

1. Water enters the seed through the Micropyle, or is absorbed by the testa through imbibition. This softens the testa and moistens the cell walls so the next stages can occur. During storage moisture levels could be low as 5% they need to get back up to 70% for germination
2. Seed cells take up water by osmosis, seed often enlarges to twice the size of dried seed. The restored water content provides suitable medium for enzymes in the process of respiration.
3. Constant supply of oxygen required for aerobic respiration to occur so that food stored in the Cotyledons or endosperm can be broken down and energy released. Without oxygen anaerobic respiration occurs and can cause death of seed.
4. The radicle emerges first and will grow downwards to form the root and begin water and mineral uptake. Geotropism ensures root grows downwards.
5. The Hypocotyl then emerges with the Plumule and will automatically grow upwards - phototropism
6. The growth of the plant is fuelled by food stored in the Cotyledons or the endosperm.
7. As soon as the first leaves form the plant is able to photosyntheize and support itself

Question 26

Epigram germination

Answer 26

Example Phaseolus vulgaris
In epigeal germination the Cotyledons become photosynthetic and are often known as seed leaves. thec2nd leaves to form arise from the Plumule.

Question 27

Hypogeal germination

Answer 27

Example Vicia faba
In hypogeal germination the Epicotyl extends and the Cotyledons stay in the ground. the Cotyledons provide a food source for seedling. First leaves form from plumule and are true leaves.