Lecture 3 Flashcards
Autotroph Definition
Assimilate radiant energy from sunlight (photosynthesis), or from inorganic compounds (chemosynthesis)
Autotroph Key Step
The energy is converted into chemical energy stored in the bonds of organic molecules
Heterotroph Definition
- 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
Holoparasites Definition/ Example
- 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
Hemiparasite Definition/Example
- photosynthetic, but obtains nutrients, water, and some of its energy from the host plant
- Ex. Mistletoe
Photosynthesis Definition
- most autotrophs
- sunlight provides the energy to take up CO2 and synthesize organic compounds
Chemosynthesis Definition
- chemolithotrophy
- Energy from inorganic compounds is used to produce carbohydrates
- important in nutrient-cycling bacteria, and in some ecosystems such as hydrothermal vent communities
Key Molecule for Most Photosynthesis
- Chlorophyll
- Leaves are green because chlorophyll the green pigment in leaves absorbs blue and red light (allowing us to see green)
What is Photosynethsis
- 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
2 Major Steps of Photosynthesis
- Light Reaction
- Dark Reaction
Light Reaction Definition
- light is harvested and used to split water and provide electrons to make ATP and NADPH
Dark Reaction Definition
- CO2 is fixed in the Calvin cycle, and carbohydrates are synthesized
Light Response Curves Definition
- show influence of light levels on photosynthetic rate
- Plants can acclimatize to changing light intensities with shifts in light response curves
Light Compensation Point Definition
- Where CO2 uptake is balanced by CO2 loss by respiration
Saturation Point Definition
- When photosynthesis no longer increases as light increases
- Shifts in light saturation point involve morphological and physiological changes
Leaves at High Light Intensity
- 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
Water Availibility
- 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
Nutrients
- 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
Rubisco
- the key enzyme for carbon fixation can catalyze two competing reactions:
1. Carboxylase reaction
2. Oxygenase reaction
Carboxylase Reaction
- photosynthesis
Oxygenase Reaction
- O2 is taken up, carbon compounds are broken down and CO2 is released (photorespiration)