Physical controls on the distribution of organisms

Question 1

Light

Answer 1

variation in light intensity is a key control in distribution of plant species within an ecosystem

Question 2

Heliophytes

Answer 2

• sun plants
• plants which grow best in full sunlight
• shade intolerant

Question 3

Sciophytes

Answer 3

• shade plants
• plants which grow best in shade
• shade tolerant

Question 4

C4 photosynthesis

Answer 4

• more efficient use of CO2
• no photorespiration
• chloroplasts concentrated within bundle sheath cells
• but expensive!
• tropical grasses
• good water-use efficiency
• efficient at high temp and low CO2

Question 5

Transpiration

Answer 5

evaporation from the leaf

Question 6

Evapotranspiration

Answer 6

evaporation from leaf plus soil

Question 7

C3 plants

Answer 7

inefficient at high temp and low CO2

• increased photorespiration
• poor water-use efficiency
• physiological drought

Question 8

CAM photosynthesis

Answer 8

Crassulacean Acid Metabolism

• carbon fixation pathway that evolved in some plants as an adaptation to arid conditions.
• closes leaves at night to reduce evapotranspiration and open at night to collect CO2

Question 9

Photoinhibition

Answer 9

shrinking of chloroplasts, loss of chlorophyll, loss of CO2 due to ‘photo-oxidation’

Question 10

Photo-respiration

Answer 10

• as a result from photo-oxidation
• CO2 released but not utilisable by plant
• only occurs in C3 plants

Question 11

Rate of photorespiration

Answer 11

positively correlated with light intensity and temperature

Question 12

Sun leaves

Answer 12

• thicker, more cell layers
• thicker cuticle
• leaves more dissected

Question 13

Shade leaves

Answer 13

• thinner, fewer cell layers
• thinner cuticle
• leaves less dissected§

Question 14

Perennials

Answer 14

live for more than 1 year

shade tolerant plants

Question 15

annuals

Answer 15

not enough light in shady conditions to support them

must germinate, grow, flower and set seed in 1 year

Question 16

phenology

Answer 16

The timing of changes in growth of plant e.g.
- flowering in spring
- Shedding leaves in Autumn
Triggered by changes in duration of daylight

Question 17

Photoperiodism

Answer 17

relationship between phenology and light

Question 18

Key points about plants and light

Answer 18

• too little light is bad, but too much light is also bad

- plants have evolved a range strategies to grow under low and high light intensities

Question 19

Temperature

Answer 19

geographic distribution of plants strongly linked to temperature
- metabolic and physical damage by extreme heat and cold

Question 20

Chilling stress

Answer 20

• damage to cold temp above 0 degrees

Question 21

Chilling sensitive

Answer 21

Damage by temp <10 degrees

Question 22

Chilling resistant

Answer 22

survive < 10 degrees but damaged by ice formation

Question 23

Frost resistant

Answer 23

survive to -15 degrees

Question 24

Frost tolerant

Answer 24

Survive to -40 degrees

Question 25

Cold tolerant

Answer 25

survive below -40 degrees

Question 26

Damage caused by chilling stress

Answer 26

- above 0 degrees, but may be 15-20 for some tropical plant species - infertile pollen or seeds - low growth rate - leaf discolouration - stem/leaf dieback - lesions on fruit - young plants affected more than older/larger plants

Question 27

Frost hardening

Answer 27

- frost resistance only possible if cooling gradual | - period of physiological preparation required

Question 28

Poikilotherms

Answer 28

- cold blooded animals - Ectotherms - fish, reptiles, amphibians, insects

Question 29

Homeotherms

Answer 29

- warm blooded animals - Endotherms - birds, mammals - metabolic generation fo heat

Question 30

Ectotherms

Answer 30

- body temp = ambient temp of environment

Question 31

Endotherms

Answer 31

- above ambient temp of environment

Question 32

Temperature Range

Answer 32

- when active, body temp must be in a narrow range | - most cannot survive close to freezing or near 40 degrees

Question 33

Eurythermic

Answer 33

species that can tolerate a broad temperature range

Question 34

Stenothermic

Answer 34

species with a restricted temperature range

Question 35

Why does metabolic rate decline rapidly above 40°C?

Answer 35

- Enzyme activity slows - Proteins break down - Cell membranes destroyed - Rates of oxygen intake no longer match respiratory needs

Question 36

Allens rule

Answer 36

the shorter an animals erctremitites are relative to body mass, the lower the rate of heat loss

Question 37

Moisture and plants

Answer 37

Xerophystes mesophytes hydrophytes

Question 38

Desert annuals

Answer 38

- 8 day life cycle | - very high rates of photosynthesis

Question 39

Tropical Deciduous trees

Answer 39

- drop leaves in dry season - store water in trunk - photosynthetic bark

Question 40

Conclusion

Answer 40

- form related to function - different strategies (avoidance versus adaptation) - interaction of physical factors