Lecture 3

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)
• The energy gain depends on the chemistry of the food, and how much effort is need to find and ingest the food
• have tremendous diversity in morphological and physiological feeding adaptations

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

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

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

What is Photosynethsis

Answer 9

• Most of the biologically available energy on Earth is derived from photosynthesis
• Photosynthetic organisms include some archaea, bacteria, and protists, and most algae and plants
• Photosynthetic rate determines the supply of energy, which in turn influences growth and reproduction
• Environmental controls on photosynthetic rate are therefore an important topic in physiological ecology

Question 10

2 Major Steps of Photosynthesis

Answer 10

1. Light Reaction
2. Dark Reaction

Question 11

Light Reaction Definition

Answer 11

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

Question 12

Dark Reaction Definition

Answer 12

• CO2 is fixed in the Calvin cycle, and carbohydrates are synthesized

Question 13

Light Response Curves Definition

Answer 13

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

Question 14

Light Compensation Point Definition

Answer 14

• Where CO2 uptake is balanced by CO2 loss by respiration

Question 15

Saturation Point Definition

Answer 15

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

Question 16

Leaves at High Light Intensity

Answer 16

• 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 17

Water Availibility

Answer 17

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

Question 18

Closing Stomates Increases _________

Answer 18

• 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 19

Nutrients

Answer 19

• 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 20

Low Nitrogen Supply

Answer 20

• relative demand for growth and metabolism

Question 21

Increasing Nitrogen Content of Leaves

Answer 21

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

Question 22

Rubisco

Answer 22

• the key enzyme for carbon fixation can catalyze two competing reactions:
  1. Carboxylase reaction
  2. Oxygenase reaction

Question 23

Carboxylase Reaction

Answer 23

• photosynthesis

Question 24

Oxygenase Reaction

Answer 24

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

Question 25

Photorespiration is sensetive to ____

Answer 25

• oxygen concentration and temperature

Question 26

Photorespiration under High Light

Answer 26

• Dissipate energy

Question 27

Photorespiration under Normal Light Conditions

Answer 27

• when plants can’t photorespire they die

Question 28

Photorespiration is a Large Disadvantage if ____

Answer 28

• CO2 is low and temperatures are high
• Such conditions existed 7 million years ago when C4 photosynthesis first appeared

Question 29

C4 Photosynthetic Pathway

Answer 29

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

Question 30

Calvin Cycle

Answer 30

• 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 31

Transpiration Losses are Minimized because ______

Answer 31

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

Question 32

Crassulacean Acid Metabolism

Answer 32

• CAM
• minimizes water loss
• Nighttime 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 33

Energy Mass per Unit

Answer 33

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

Question 34

Crossbills

Answer 34

• 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 35

Multicellular Animals

Answer 35

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

Question 36

Why do Orangutans have Longer Digestive Systems

Answer 36

• to have more opportunities to absorb nutrients from their plant material (which is poor nutrients/ harder to absorb)
• Plant material is harder to digest than animals

Question 37

Tools and Energy Gain

Answer 37

• Humans view toolmaking as something that differentiates us from other animals
  -Toolmaking in chimpanzees has been known since the 1920’s

Question 38

Examples of Animals that Make Tools

Answer 38

• 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

Question 39

How is Knowing Isotopic Compositions of Food Sources a Tool?

Answer 39

• it provides a tool to infer diet