Plant Physiological

Question 1

Physiological ecology is different
for plants because they are

Answer 1

Sessile, with little scope for behaviour; animals
can escape adverse conditions, but plants must
tolerate them
* Autotrophic; they make their own food through
photosynthesis
* All plants need the same few things to grow:
light, CO2 , water, and soil nutrients (especially
nitrogen, phosphorus, and potassium, or NPK)

Question 2

Photosynthesis

Answer 2

• Plants must bring together CO2 , water, and light
  in functioning photosynthetic tissues
• Enzymes also require an OK temperature
• For growth, plants have to acquire more carbon
  through photosynthesis than they lose through
  respiration; carbon balance is therefore key

Question 3

Net primary productivity (NPP)

Answer 3

C gained via photosynthesis – C lost via respiration = NPP

Question 4

Photosynthetic structures embody
adaptation to environmental stresses

Answer 4

Photosynthetic
(green) structures
are usually leaves
(but can be stems)
* Plants take in CO 2
through stomata
* But plants also
transpire; they
lose water through
stomata (singular
stoma)

Question 5

Photosynthetic structures embody
adaptation to environmental stresses

Answer 5

Leaf size and shape: SA:V ratios important
again
* Benefits of large leaf surface area: good for
harvesting light, CO2
* Costs of large leaf surface area: bad for
overheating, water loss by transpiration
through stomata

Question 6

How do plants cope with
overheating/water loss?

Answer 6

Most plants fix carbon by C 3 photosynthesis
* Rubisco is the enzyme that accepts CO2
* But at high temperatures, Rubisco often captures
O 2 instead of CO 2 , which is bad for plants
(“photorespiration”)

Question 7

C4 Photosynthesis

Answer 7

the enzyme PEP carboxylase
first accepts CO2 , reducing photorespiration

Question 8

CAM photosynthesis

Answer 8

plants close stomata during
the day to reduce water loss, open stomata at
night to let in CO 2 ; photosynthesis still needs
light, so they store CO2 as malate until daytime

Question 9

Plants with large leaves also
combat overheating by:

Answer 9

Growing in shady habitats
* Evaporative cooling by opening stomata

Question 10

Evaporative cooling needs plentiful water—
not always available. Plants with large leaves
combat water loss by:

Answer 10

Closing stomata…
* …but that shuts off all gas exchange, including
CO2 input, so photosynthesis shuts down. Plant
stops growing…
* …and risks overheating & tissue damage
* Therefore, fundamental trade-off between water
conservation and rapid growth
* Consequences most obvious in desert plants

Question 11

Palo Verde

Answer 11

Palo Verde = “green stick”
Photosynthetic bark on trunks & branches; can grow without
incurring heat load & water loss through leaves

Question 12

Saguaro cactus

Answer 12

Grows to 15 m,
200 yr, 5+ tonnes
* CAM photosynthesis
* Extensive, shallow roots
* Accordion-pleated trunk
allows expansion
* Can absorb 800 L of water
from one storm, use it
gradually for growth
* Mnemonic digression for
water storage: David
Grundman (d. 1982)

Question 13

Tropical trees

Answer 13

also extensive but
shallow roots
Tropical rainforests have a shallow layer of nutrient-rich soil
* Extensive, shallow roots are an adaptation to acquire scarce
nutrients (phosphorus, nitrogen, etc.)

Question 14

Deciduous habit

Answer 14

dropping leaves during dry or cold
seasons reduces water stress and tissue damage

Question 15

Epiphytes

Answer 15

grow on trees,
so they aren’t able to put
their roots into the soil,
leading to water stress
and nutrient shortages