TOPIC 7: PLANT ADAPTATIONS

Question 1

Photosynthesis

Answer 1

process where energy from the sun is used to transform CO2 into
carbohydrates (simple sugars) and O2

Chlorophyll (light absorbing pigment) traps light energy → synthesizes ATP →
this energy drives CO2 → O2 + sugars

Question 2

Where does photosynthesis take place?

Answer 2

takes place in specialized cells (mesophyll cells) in the leaf

Question 3

rubisco

Answer 3

enzyme that catalyzes part of the photosynthetic reaction
- makes rxn happen after

• more of it= faster rxn

Question 4

• Respiration:

Answer 4

: in the mitochondria of cells (plant & animal) - carbohydrates are broken down to generate energy (ATP), releasing CO2

Question 5

Net Photosynthesis

Answer 5

Plants both use and produce CO2 and the difference in the rates of these two processes
is:

Net Photosynthesis = Photosynthesis – Respiration
* (= carbon uptake – carbon loss)

Question 6

stomata

Answer 6

openings in the leaf thru which CO2 diffuses into the leaf

Question 7

transpiration

Answer 7

• CO2 enters: atmosphere&raquo_space; leaf
• Water leaves: atmosphere &laquo_space;leaf

Question 8

What essential resources do plants require?

Answer 8

light, CO2, water, nutrients

Question 9

Leaf tissue

Answer 9

• photosynthesis (uptake of CO2)

Question 10

Stem tissue

Answer 10

• structural support (gain access to light)

Question 11

Root tissue

Answer 11

• water and nutrient uptake from the soil

Question 12

Compare the adaptations that plants have at the tree top vs tree bottom

Answer 12

• Tree Top (direct sunlight)
• smaller, thicker leaves
  → reduces water loss in direct sunlight
• Tree bottom (shade)
• larger, thinner
  → increases photosynthetic rate in shade

Question 13

Plants are either…..

Answer 13

to low light (shade-tolerant) or high light (shade-intolerant)

Question 14

Shade-tolerant (low light):

Answer 14

In shade: photosynthesis is limited by availability of light
* lower production of rubisco in leaf tissue (do not expend energy producing high amounts of rubisco)
Lower maximum photosynthetic rate

Question 15

How do shade tolerant plants compensate?

Answer 15

• higher production of chlorophyll (light absorbing pigment)
• higher leaf surface area
• higher growth of leaves than roots
• increase the photosynthetic surface area to offset the decrease in
  photosynthetic rate (due to lower amount of rubisco)

Question 16

What happens to the plant growth if you put a shade intolerant plant in the shade vs if you put a shade tolerant plant in the sun?

Answer 16

• Shade-intolerant - high growth rates under sunlight, but low rates in shade
• Shade-tolerant - grow similarly under sunlight and shade
• cannot increase growth dramatically in sunlight because limited by rates of
  photosynthesis (lower concentration of rubisco)

Question 17

Mountain Avens

Answer 17

Flowers track the movement if the sun
- Parabolic formation of petals concentrate light to maintain a constant temperature of
25⁰C.
- Keeps sex organs of the plant warm and creates a microhabitat favourable for
pollinators

Question 18

Mountain Avens

Answer 18

Flowers track the movement if the sun
- Parabolic formation of petals concentrate light to maintain a constant temperature of
25⁰C.
- Keeps sex organs of the plant warm and creates a microhabitat favourable for
pollinators

Question 19

Plants vs. Temperature

Answer 19

Photosynthesis and respiration respond directly to variations in temperature
* As temperatures rise above 0, rates of both respiration and photosynthesis increase
* A maximum rate of photosynthesis and respiration occur at different points
* Proteins denature and both processes stop eventually

Question 20

What must a leaf do to maintain optimal levels of photosynthesis?

Answer 20

must exchange excess heat with the
surrounding environment

Question 21

Heat loss by convection

Answer 21

transfer of heat to a moving fluid body (ie. Wind)

Question 22

Heat loss by conduction

Answer 22

• Heat moving from a warmer to a cooler body

Question 23

Heat loss by evaporation

Answer 23

Evaporation causes a loss of heat energy and temperatures drop due to
evaporative cooling

Question 24

Pubescence

Answer 24

small light-coloured hairs that line a leaf’s surface and reflect
- Less heat obtained from solar radiation
- Also creates a insulative boundary later

Question 25

Skunk cabbage

Answer 25

• Metabolically generates heat in the spring to thaw snow and attract pollinator
• Endothermic plant

Question 26

Accumulation of compounds

Answer 26

• Sugars, amino acids (proline) and other solutes
• Lowers the freezing point of water to prevent ice formation

Question 27

Supercooling

Answer 27

• Special anti freeze proteins preventing ice crystal growth allowing plants to
  survive up to -35C
• Present in floral and shoot buds

Question 28

frost hardening

Answer 28

Changes composition of membranes allowing cells to export water and ice to
form between cells instead of within
* Allows survival up to -50C

Question 29

Deciduous Trees

Answer 29

• Adaptive loss of leaves as the temperature drops in the fall months
• Programmed death to survive the winter when the leaves would freeze

Question 30

Plants vs. Water Availability

Answer 30

• Plants have evolved a range of adaptations in response to the variability of precipitation
  and soil moisture
• When the atmospheric humidity and soil moisture levels are low plants will close their
  stomata
• Can also occur on a daily basis, where mid day, stomata close to conserve water
• Remain open during the mornings and later afternoon

Question 31

1. Short time scales:

Answer 31

Regulate opening and closing of stomata during different parts of the day
e.g. close stomata during hottest part of the day when highest water loss through evaporation
* Leaf curling or wilting – reduces the surface area of the leaf exposed to solar
radiation and, thus, water loss

Question 32

2. Moderate time scales:

Answer 32

• Individuals can balance leaf vs root tissue
• Wet conditions (ideal) → ↑ leaf tissue & ↓ root and shoot
• Increase the photosynthetic surface (maximizes CO2 uptake and
  photosynthetic rates → growth)
• No increase in other tissues (i.e. shoot, root) because this
  increases the rate of respiration (CO2 loss)
• Dry conditions → ↑ root tissue & ↓ leaf and shoot
• Increases the volume of tissue in the soil to extract water
  Reduces the surface area of leaf tissue to reduce water loss

Question 33

Long time scales:

Answer 33

• leaf morphology adaptations to dry conditions:
• smaller and thicker leaves (water storage)
• smaller stomata
• cover leaves in wax, resin, little hairs (e.g. cactus)
• Some species have alternative photosynthetic pathways
• C4 photosynthesis
• 3% of plants, common in grasses
• CAM photosynthesis
• 7% of plants, common in epiphytes and cacti
• Add an extra step in the conversion of CO2 into an organic acid before entering
  Calvin cycle (dark reactions)