Lecture 3: Coping with Environmental Variation - Energy

Question 1

Autotroph Definition

Answer 1

Assimilate radiant energy from sunlight (photosynthesis), or from inorganic compounds (chemosynthesis)

Question 2

Autotroph Key Step

Answer 2

The energy is converted into chemical energy stored in the bonds of organic molecules

Question 3

Heterotroph Definition

Answer 3

• Obtain their energy by consuming organic compounds from other organisms
• consume energy-rich organic compounds (food) and convert them into usable chemical energy (ATP)

Question 4

Holoparasites Definition/ Example

Answer 4

• They have no photosynthetic pigments and get energy from other plants (heterotrophs)
• Ex. Dodder: is an agricultural pest and can significantly reduce biomass in the host plant

Question 5

Hemiparasite Definition/Example

Answer 5

• photosynthetic, but obtains nutrients, water, and some of its energy from the host plant

Ex. Mistletoe

Question 6

Photosynthesis Definition

Answer 6

• most autotrophs
• sunlight provides the energy to take up CO2 and synthesize organic compounds

Question 7

Chemosynthesis Definition

Answer 7

• Energy from inorganic compounds is used to produce carbohydrates
• important in nutrient-cycling bacteria, and in some ecosystems such as hydrothermal vent communities
• Ex. Ammonium and nitrate

Question 8

Key Molecule for Most Photosynthesis

Answer 8

• Chlorophyll
• Leaves are green because chlorophyll the green pigment in leaves absorbs blue and red light (allowing us to see green)

Question 9

Photosynthesis - light reaction

Answer 9

• Light is harvested and used to split water and provide electrons to make ATP and NADPH

Question 10

Photosynthesis - dark reaction

Answer 10

• CO2 fixed in the Calvin cycle
• Carbohydrates are synthesized

Question 11

Photosynthetic rate

Answer 11

• determines the supply of energy, which in turn influences growth and reproduction

Question 12

Light Response Curves Definition

Answer 12

• show influence of light levels on photosynthetic rate
• Plants can acclimatize to changing light intensities with shifts in light response curves

Question 13

Light Compensation Point Definition

Answer 13

• Where CO2 uptake is balanced by CO2 loss by respiration

Question 14

Saturation Point

Answer 14

• When photosynthesis no longer increases as light increases
• Shifts in light saturation point involve morphological and physiological changes

Question 15

Leaves at High Light Intensity

Answer 15

• may have thicker leaves and more chloroplasts
• When light hits the leaf it is absorbed by the top layer, and by the time the light reaches the bottom of the thick layer there isn’t much light energy left

Question 16

Water Availability

Answer 16

• influences CO2 supply in terrestrial plants
• Low water availability causes stomates to close, restricting CO2 uptake
• Trade-off: water conservation versus energy gain

Question 17

Closing Stomates

Answer 17

• Increases the chances of light damage
• If the calvin cycle isn’t operating, energy builds up in the light-harvesting arrays and can damage membranes

Question 18

Nutrients

Answer 18

• Can affect photosynthesis
• Most nitrogen in plants is associated with photosynthetic enzymes (e.g. rubisco)
• Higher nitrogen levels in a leaf are correlated with higher photosynthetic rates

Question 19

Low Nitrogen Supply

Answer 19

• relative demand for growth and metabolism

Question 20

Increasing Nitrogen Content of Leaves

Answer 20

• increases the risk that herbivores will eat them, as plant-eating animals are also nitrogen-starved
• Some metabolic processes decrease photosynthetic efficiency

Question 21

Rubisco

Answer 21

the key enzyme for carbon fixation can catalyze two competing reactions:

1. Carboxylase reaction
2. Oxygenase reaction

Question 22

Carboxylase Reaction

Answer 22

photosynthesis

Question 23

Oxygenase Reaction

Answer 23

O2 is taken up, carbon compounds are broken down and CO2 is released (photorespiration)

Question 24

Photorespiration under High Light

Answer 24

• Dissipate energy
• protects plants from damage

Question 25

Photorespiration under Normal Light Conditions

Answer 25

when plants can’t photorespire they die

Question 26

Photorespiration is a Large Disadvantage if ____

Answer 26

CO2 is low and temperatures are high

Question 27

C4 Photosynthetic Pathway

Answer 27

• reduces photorespiration, and evolved independently several times
• Many grass species use this pathway (corn, sugarcane, and sorghum)
• Involves biochemical and morphological specialization

Question 28

Calvin Cycle

Answer 28

• vulnerable to low CO2 conditions
• CO2 uptake and the Calvin cycle occur in different parts of the leaf
• CO2 is taken up in the mesophyll by PEPcase (which has greater affinity for CO2 , and does not take up O2)
• CO2 concentration is increased in bundle sheath cells where rubisco is operating in the Calvin cycle (which reduces O2 uptake by rubisco)

Question 29

Transpiration Losses are Minimized because ______

Answer 29

• PEPcase can take up CO2 even when stomates are not fully open

Question 30

Crassulacean Acid Metabolism (CAM)

Answer 30

• minimizes water loss
• At night is the best time to open stomata because it’s cooler and more humid
• During the day, stomates are closed because it is too hot
• CO2 uptake and the calvin cycle are separated temporally
• CAM plants are often succulent, with thick, fleshy leaves or stems (common in arid environments)

Question 31

Energy Mass per Unit

Answer 31

Highest: Fats
Carbs
Proteins (but contain N)
Fibre (indigestible)
Lowest: Secondary compounds (can interfere with digestion)
- Feeding strategies are very diverse among heterotrophs

Question 32

Crossbills

Answer 32

• Each incipient species shows an adaptive peak in association with the conifer species it preferentially feeds on
• Inside cones, there are very valuable, nutrient-rich seeds
• Crossbill is used to take the husk off the seed inside cones (such as pinecones)
• Therefore the beak of a crossbill is actually an advantage

Question 33

Multicellular Animals

Answer 33

• Have evolved specialized tissues and organs for absorption, digestion, transport, and excretion
• Compared with omnivorous humans, herbivorous primates have longer digestive systems

Question 34

Examples of Animals that Make Tools

Answer 34

• Crows on the South Pacific Island use tools to snag insects from decomposing trees
• Dolphins have a learned behaviour called sponging, using another organism to protect them from getting stung at the bottom of the ocean floor