Plant adaptions

Question 1

What is the consequence of diverse plants?

Answer 1

Diversity of plants consequence of different
evolutionary solutions to common problems of
acquiring the resources which support photosynthesis.

Question 2

What is photosynthesis?

Answer 2

Light (PAR*) + Nutrients + CO2 + H2O → C6H12O6 +
O2 + H2O
▪ Availability of light directly influences the rate of photosynthesis
▪ An increase in PAR leads to increase in rate of photosynthesis

Question 3

What is respiration?

Answer 3

C6H12O6 + O2 → CO2 + H2O + ATP
▪ In the dark only respiration occurs, and CO2 is lost.

O2 from photosynthesis is used for respiration.

Question 4

How does photosynthesis involve exchanges between
the plant and atmosphere?

Answer 4

▪ Photosynthesis takes place in mesophyll cells in the leaf.
▪ CO2 moves from the atmosphere into the leaf via stomata.
▪ the flow rate of CO2 through the stomata is determined by.
▪ stomatal density.
▪ aperture.
▪ Stomata are not always open.

Question 5

How does Water Move from the Soil, through the
Plant, to the Atmosphere?

Answer 5

▪ Plants function best when their cells are fully hydrated.
▪ The rate of transpiration varies daily.
▪ Controlling the stomata is a plant’s most important way to regulate water loss
▪ Trade-off: taking in CO2 for photosynthesis vs losing water needed to live.
▪ Directly influences the productivity of different ecosystems with different environmental conditions.

Question 6

How does The Process of Carbon Uptake Differ for
Aquatic and Terrestrial Autotrophs?

Answer 6

▪ Aquatic autotrophs don’t have stomata
▪ CO2 diffuses from the water across the cell membrane directly into the cell
▪ Why is this different to terrestrial plants?
▪ Susceptible to CO2 depletion.
▪ Why?

Question 7

How does Plant Temperatures Reflect Their Energy Balance with the Surrounding Environment?

Answer 7

▪ Both photosynthesis and cellular respiration increase as temperature increases.
▪ Internal leaf temperature may sometimes be much higher than air temperature and may reach critical levels.
▪ Plants must therefore lose heat:

1. Evaporation
2. Convection
3. Heat loss

Question 8

Evaporation

How does Plant Temperatures Reflect Their Energy Balance with the Surrounding Environment?

Answer 8

part of transpiration
* Evaporative cooling increases with increase in the rate of transpiration.
* Terrestrial plants.

Question 9

Convection

How does Plant Temperatures Reflect Their Energy Balance with the Surrounding Environment?

Answer 9

Transfer of heat energy through the circulation of air (wind) or water (currents)
▪ Terrestrial & aquatic plants.
▪ Prevents the boundary layer from getting too thick.
* this prevents the transfer of heat, water and CO2 between the leaf and the environment.

Question 10

Heat Loss

How does Plant Temperatures Reflect Their Energy Balance with the Surrounding Environment?

Answer 10

Increased by
interrupting the boundary
layer by modifying leaf
size and shape.

▪ The physical environment affects how plants lose heat:
▪ Areas of high water-availability.
- most heat is lost through transpiration.
▪ Areas of lower water availability.
- transpiration is limited
- other stuff not on slide

Question 11

What is a boundary layer?

Answer 11

the layer of still air (or
water) next to the leaf surface.
It doesn’t move.
inhibits the loss of water through transpiration.

Question 12

What is trade-off?

Answer 12

Plants must balance water loss vs heat gain.

Question 13

What Constraints Imposed by the Physical Environment Have led to a Wide Array of Plant Adaptations?

Answer 13

▪ To survive, plants must acquire essential resources while tolerating environmental conditions.
▪ Features of physical environment often interdependent

▪ In dry, sunny environments
▪ greater PAR
▪ lower humidity

Question 14

How would plants adapt structurally to a dry & sunny environment or a cool & wet environment?

Question 15

How would plants deal with conflicting needs above- and below ground?

Question 16

What is The Link between Water Demand and
Temperature Influences Plant Adaptations?

Answer 16

1. Modifications to stomata
2. Modifications to root: leaves
3. Modification to photosynthetic pathways
4. Changes in leaf size and shape.
5. Curling or wilting leaves
6. Chlorophyll production is inhibited and leaves turn yellow if water stress is prolonged
7. Plants may be drought deciduous

Question 17

Modifications to stomata

What is The Link between Water Demand and
Temperature Influences Plant Adaptations?

Answer 17

▪ The demand for water is related to temperature
▪ air temperature rises → rate of transpiration (& water-loss) rises.
▪ Plants modify open/close cycle of stomata.

• closed or partially closed
• when atm and soil is dry
• during the hottest part of the day
• open only during early morning or at night.
• cooler or more humid conditions

▪ Plants modify size & density of stomata.

What are the consequences to the plant?

Question 18

Modifications to energy put into the development of root: leaves

ratio of roots to leaves

What is The Link between Water Demand and
Temperature Influences Plant Adaptations?

Answer 18

▪ Proportionate allocation of carbon to roots & leaves depends on prevailing conditions during early development. (when it is very dry)

▪ Plant compensates to maximise acquisition of scarce resource or to take advantage of abundant resource.

• More roots and less leaves allows plants to explore more soil for extracting water.
• Reducing leaf area decreases the amount of solar radiation striking the plant and decrease the surface are across which is lost through transpiration.

[ shrubs and grasslands have more roots than shoots than forest and woodlands ]

Question 19

Modifications to photosynthetic pathways.

What is The Link between Water Demand and
Temperature Influences Plant Adaptations?

Answer 19

▪ C3 plants – in areas without water limitation
▪ C4 plants– increased efficiency of water use in warmer and drier environments.

[ different photosynthetic plants use a different water pathway ]

Question 20

Changes in leaf size and shape.

What is The Link between Water Demand and
Temperature Influences Plant Adaptations?

Answer 20

▪ In dry environments leaves tend to be
- smaller and thicker (more cells in the same unit area)
- covered in hairs that scatter solar radiation
- coated with waxes and resins that reflect light and reduce absorption.

Question 21

Curling or wilting leaves

What is The Link between Water Demand and
Temperature Influences Plant Adaptations?

Answer 21

• reduces leaf area exposed to the sun.
• reduces water loss and heat gain.

Question 22

Chlorophyll production is inhibited and leaves turn
yellow if water stress is prolonged

What is The Link between Water Demand and
Temperature Influences Plant Adaptations?

Answer 22

• Deciduous trees prematurely shed leaves

Question 23

Plants may be drought deciduous

What is The Link between Water Demand and
Temperature Influences Plant Adaptations?

Answer 23

• Drop their leaves at start of dry season.
• New leaves grow just before the rainy season begins.

Question 24

how do Plants Exhibit Both Acclimation and Adaptation in Response to Variations in Environmental Temperatures?

Answer 24

▪ Plants are exposed to wide variations in temperature on many spatial and time scales
▪ All plants experience daily & seasonal changes in
temperature.

Question 25

NB slide 26-29 graphs

Answer 25

Tmin, Topt, and Tmax varies

Question 26

Periods of extreme heat or cold can damage plant
cells and tissues therefore plants have cold specific adaptions explain.

how do Plants Exhibit Both Acclimation and Adaptation in Response to Variations in Environmental Temperatures?

Answer 26

Adaptations by cold-tolerant plants:
▪ frost hardening - genetic ability to tolerate extreme cold; variable within and among species
▪ Special compounds allow leaves to survive freezing temperatures
- E.g. needle leaf evergreens (pine and spruce)
▪ winter deciduous species - shed their leaves before the beginning of the cold season.

Question 27

How are Species of Plants Are Adapted to Different
Light Environments?

Answer 27

▪ Shade intolerant (sun loving) plants– adapted to
high-light environments
▪ Shade tolerant plants– adapted to low-light environments
▪ Show fundamental differences in patterns of photosynthesis in response to different
levels of available light

Question 28

How are shade tolerant plants adapted?

How are Species of Plants Are Adapted to Different Light Environments?

Answer 28

▪ More chlorophyll per cell
▪ Larger leaf area
▪ Root < shoot (leaf + stems)
▪ Tend to be evergreen.

Question 29

Can plants adapted for shade adapt to sunny conditions and vice versa?

How are Species of Plants Are Adapted to Different Light Environments?

Answer 29

Shade loving plants can tolerate the sun - slight increase in growth when in the sun, but doesn’t ever grow as much as sun loving plants grow, it cannot capitalise on the amount of sun available.
But the sun loving plants cannot tolerate living in the shade - increase in mortality in the shade.

Question 30

How do Plants Exhibit Adaptations to Variations in Nutrient Availability?

Answer 30

▪ Chemical elements needed for metabolic processes and to synthesise new tissues
▪ Macronutrients
▪ C, H, O (major component of plants)
▪ derived from CO2 and H2O
▪ N, P, K, Ca, Mg, S
▪ Micronutrients (trace elements)
▪ E.g., Cl, Fe, Mn

▪ Rate of nutrient absorption depends on nutrient concentrations in the soil or water
▪ a decrease in nutrient concentrations in the environment eventually reduces maximum rate of photosynthesis by leaves

Question 31

How do plants respond to reduced nutrient availability?

Plants Exhibit Adaptations to Variations in
Nutrient Availability

Question 32

What are the Other adaptations to low- nutrient environments include?

Plants Exhibit Adaptations to Variations in
Nutrient Availability

Answer 32

▪ Symbiosis with N-fixing bacteria
▪ increased leaf life span
▪ lower growth rate

Question 33

What are Ecological Issues & Applications: Plants Respond to Increasing Atmospheric CO2?

Answer 33

▪ The CO2 fertilization effect
▪ as atmospheric [CO2] increases, the diffusion gradient between the air and the interior of the leaf increases
- more CO2 moves into the leaf
▪ increased [CO2] in mesophyll cells will increase the rate of photosynthesis & reduce
photorespiration
- enhances potential rates of…
▪ Short term response – aperture size smaller (stomata partially close)
▪ Longer term response –stomata density decrease (developmental plasticity)
▪ Seen in ≤ 22% across all species grown under 567
ppm CO2 (~1.5 current)
▪ More pronounced in grasses and herbaceous crops than in trees and shrubs
▪ reduce the rate of transpiration - increase water-use efficiency

Question 34

What about the effect of long-term exposure to elevated CO2 levels?

Ecological Issues & Applications: Plants Respond to Increasing Atmospheric CO2

Answer 34

▪ Average increase in biomass in > 600 experiments:
▪ C3 plants – strongest response – 47%
▪ CAM (desert-adapted) plants – based on six species – 21%
▪ C4 plants – 11%

Question 35

Will these enhanced effects on plant growth persist?

Ecological Issues & Applications: Plants Respond to Increasing Atmospheric CO2

Answer 35

Probably short lived:
- photosynthesis rate may decline to previous level
- plants may reallocate carbon, produce fewer leaves and more roots
- nutrient levels in plant may decrease