Chapter 28 - Growth And Development

Question 1

Define development

Answer 1

The stage of growth which includes changes in structure and appearance of cells

Question 2

Define germination

Answer 2

Is the onset of growth of the embryo plant in a seed after period of dormancy

Question 3

Conditions necessary for germination

Answer 3

1. Water
2. Suitable temperature
3. Oxygen
   Note: no soil, light or CO2

Question 4

Method of measuring growth in herbaceous plants

Answer 4

1. Plant a large number of seeds
2. Every week remove a sub-sample
3. Wash and remove all soil
4. Heat seedlings in oven at 60 - 110 *C
5. Then weigh and reheat and reweigh until mass is constant
6. No water is left only dry-mass
7. Cool in desiccator and calculate average

Question 5

Method of measuring growth in mammal

Answer 5

1. Measure height or length

2. Weigh the body

Question 6

Advantages of measuring growth

Answer 6

• quick and easy
• does not damage organism
• can be used in the field

Question 7

Disadvantages of measuring growth

Answer 7

• lengths can vary with an increase in mass

- measure on direction only

Question 8

Advantages of measuring dry mass

Answer 8

• gives best accurate measurements
• not influenced by water
• reflects permanent increase in mass
• not influenced by variation in growth

Question 9

Disadvantages of measuring dry mass

Answer 9

• time consuming

- kills organism

Question 10

Advantages of measuring wet mass

Answer 10

• a quick process
• does not kill organism
• gives more accurate reading

Question 11

Disadvantages of measuring wet mass

Answer 11

• plants must be uprooted
• difficult to measure large organisms
• amount of water in body is a variable

Question 12

Define seed dormancy

Answer 12

When water level decreases the seed moves into a dormancy period which causes a seed to have a very slow metabolic rate and then germination will not occur

Question 13

Advantages of seed dormancy

Answer 13

• allows seed to survive unfavourable conditions
• prevents germination in brief warm spell
• prevents germination before seed dispersal
• allows time for embryo to mature

Question 14

Breaking seed dormancy

Answer 14

• seeds contain plant hormones that prevent or promote germination
• the first is called abscisic acid
• prevents germination
• abscisic acid occurs inside or outside the testa
• must be washed out
• only heavy showers can lead to germination
• the second is called gibberellin
• promotes germination
• made in embryo diffuses out to aleurone layer to produce enzymes
• enzymes digest nutrients

Question 15

Stages in germination

Answer 15

1. Seed takes up water
2. Cotyledon swells causing testa to burst
3. Enzymes become active
4. Enzymes digest insoluble nutrient
5. Digested nutrients diffuse to embryo for respiration and growth
6. Radicles emerge through micropyle
7. Testa falls off
8. Plumule emerges from seed
9. Plumule opens and shoots grow
10. Shoots carry out photosynthesis

Question 16

Define growth

Answer 16

The permanent increase in size and number of cells which takes place as cells absorb, expand and divide