Coping with Environmental Variation pt.2

Question 1

Autotrophs

Answer 1

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

Question 2

Heterotrophs

Answer 2

Obtain their energy by consuming organic compounds from other organisms.

Question 3

Energy

Answer 3

Key step: The energy is converted into chemical energy stored in the bonds of organic molecules
This energy originated with organic compounds synthesized by autotrophs
Some consume nonliving organic matter
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
Parasites and herbivores consume live hosts but do not necessarily kill them
Predators capture and consume live prey animals

Question 4

Holoparasites

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

Answer 5

photosynthetic, but obtains nutrients, water, and some of its energy from the host plant
Ex. Mistletoe

Question 6

Photosynthesis

Answer 6

(most autotrophs): sunlight provides the energy to take up CO2 and synthesize organic compounds

Question 7

Chemosynthesis (chemolithotrophic)

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

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

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: light is harvested and used to split water and provide electrons to make ATP and NADPH.
2. Dark reaction: CO2is fixed in the Calvin cycle, and carbohydrates are synthesized

Question 11

Light response curves

Answer 11

Show the influence of light levels on the photosynthetic rate.

Question 12

Light compensation point

Answer 12

Where CO2 uptake is balanced by CO2 loss by respiration

Question 13

Saturation Point

Answer 13

When photosynthesis no longer increases as light increases.

Plants can acclimatize to changing light intensities with shifts in light response curves
Shifts in light saturation point involve morphological and physiological changes

Question 14

Leaves at high light intensity

Answer 14

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 15

Water Availability

Answer 15

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
Closing stomates 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
Plants have various mechanisms to dissipate this energy, including carotenoids
Plants deal with excess energy through other pigments
Plants from different climate zones have enzyme forms with different optimal temperatures allowing them to operate in that climate
Plants can acclimatize by synthesizing different enzyme forms

Question 16

Nutrients

Answer 16

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
Low Nitrogen Supply: relative demand for growth and metabolism
Increasing Nitrogen Content of Leaves increases the risk that herbivores will eat them, as plant-eating animals are also nitrogen-starved
Some metabolic processes decrease photosynthetic efficiency

Question 17

Rubisco

Answer 17

the key enzyme for carbon fixation can catalyze two competing reactions:
Carboxylase reaction: photosynthesis
Oxygenase reaction: O2 is taken up, carbon compounds are broken down and CO2 is released (photorespiration)
Photorespiration is: Sensitive to oxygen concentration and temperature

Question 18

Does Photorespiration Have Benefits

Answer 18

Under high light, dissipate energy
Under normal light conditions, when plants can’t photorespire, they die
Experiments with arabidopsis thaliana plants with a mutation knocks out photorespiration
Plants die under normal light and CO2 conditions
Photorespiration is a large disadvantage if CO2 is low and temperatures are high
Such conditions existed 7 million years ago when C4 photosynthesis first appeared
C4 photosynthetic pathway: reduces photorespiration and evolved independently several times
Many grass species use this pathway (corn, sugarcane, and sorghum)
Involves biochemical and morphological specialization

Question 19

Calvin Cycle

Answer 19

Calvin cycle is 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

More ATP is required for the C4 pathway
higher photosynthetic efficiency gives these plants an advantage at high temperatures
Transpiration losses are minimized because PEPcase can take up CO2 even when stomates are not fully open

Question 20

Crassulacean Acid Metabolism

Answer 20

(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
Some occur in the humid tropics—mostly epiphytes that grow on tree branches and have less access to water.

Question 21

Energy Mass Per Unit

Answer 21

Highest: Fats
Carbs
Proteins (but contain N)
Fibre (indigestible)
Lowest: Secondary compounds (can interfere with digestion)
Feeding strategies are very diverse among heterotrophs
Soil microorganisms that feed on detritus invest little energy to find food, but the food has low energy content.

Question 22

Crossbills

Answer 22

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 23

Multicellular Animals

Answer 23

Have evolved specialized tissues and organs for absorption, digestion, transport, and excretion
Compared with omnivorous humans, herbivorous primates have longer digestive systems
Plant material is harder to digest than animals
Orangutans have a longer digestive system to have more opportunities to absorb nutrients from their plant material (which is poor nutrients/ harder to absorb)

Question 24

Tools and Energy Gain

Answer 24

Humans view toolmaking as something that differentiates us from other animals
Toolmaking in chimpanzees has been known since the 1920’s
Some birds also make tools:
Ex. Crows on the South Pacific Island use tools to snag insects from decomposing trees
Ex. Dolphins have a learned behaviour called sponging, using another organism to protect them from getting stung at the bottom of the ocean floor
Knowing the isotopic composition of food sources provides a tool to infer the diet