Chapter 6 Flashcards
Define autotrophs
An organism that can synthesise its own organic compounds from inorganic materials.
Autotrophs may be of two types
phototrophs – use light as their energy source
chemotrophs – use the oxidation of chemical compounds as their energy source
Define photosynthesis
photosynthesis, the process of transforming sunlight energy into chemical energy. During photosynthesislight energy is captured and used to convert water and carbon dioxide, into oxygen and glucose.
What is the photosynthesis equation?
6CO2 + 6H2O → C6H12O6 + 6O2.
Define stomata
Stomata are small pores found in the epidermis of leaves, stems and other plant organs. Stomata allow gases such as carbon dioxide, water vapour and oxygen to diffuse into and out of the internal tissues of the plant.
Define chloroplasts
Chloroplasts are organelles that conduct photosynthesis, where the photosynthetic pigment chlorophyll captures the energy from sunlight and converts it into chemical energy. They have an inner, and outer membrane
Define thylakoid
Thylakoids are membrane-bound flat disks inside chloroplasts. They are the site of the light-dependent reactions of photosynthesis. Thylakoids consist of a thylakoid membrane surrounding a thylakoid lumen. Chloroplast thylakoids frequently form stacks of disks referred to as grana. They have chlorophyll embedded in their membrane
Define chlorophyll
A chemical found in the thylakoids of chloroplasts. It is responsible for absorbing light energy in photosynthesis
Define Granum (pl.Grana)
A stack of thylakoids
Define stroma
The fluid substance, filled with many enzymes and solutes, that makes up the interior of the chloroplasts. It is the site of the light-independent stage of photosynthesis
What is endosymbiosis theory, and what is the evidence that supports it?
The Endosymbiotic Theory states that the mitochondria and chloroplast in eukaryotic cells were once aerobic bacteria (prokaryote) that were ingested by a large anaerobic bacteria (prokaryote). This theory explains the origin of eukaryotic cells.
Numerous lines of evidence exist, including that mitochondria and chloroplasts have their own circular DNA (prokaryotes also have circular DNA), mitochondria and chloroplasts have a double membrane, They have their own ribosomes that share characteristics with bacterial ribosomes, They are a similar size to bacteria, Chloroplasts and bacteria both replicate through binary fission
What occurs in the light dependent stage of photosynthesis
The Light Dependent Stage:
Occurs in the grana of a chloroplast
Chlorophyll absorbs light energy
Electrons in chlorophyll become excited
Electrons move through the electron transport system, pumping hydrogen ions into the thylakoid space
The light energy is also used to split water:
water hydrogen ions + oxygen+ electrons
The oxygen is released from the chloroplast
This sets up an ion gradient which is used to make ATP
NADP (Nicotinamide Adenine Dinucleotide Phosphate) accepts spent electrons and hydrogen ions and becomes NADPH
What occurs in the light independent stage of photosynthesis
Occurs in the stroma of a chloroplast
Sugar is produced via the Calvin-Benson Cycle
Uses CO2, H+ and ATP
NADPH provides the H+ (picked up from the stroma)
ATP created in the light dependent stage provides the energy for this stage
- Carbon dioxide molecules enter the light independent stage which is powered by ATP. During these reactions, the Carbon atoms of the CO2 molecules form chains, eventuating in glucose molecules
- NADPH formed in the light- dependent reactions unload their hydrogen ions and electrons to produce glucose
- The additional oxygen molecules from CO2 and hydrogen ions from NADPH bind together to create water
How does carbon dioxide concentration affect photosynthesis?
Carbon dioxide - with water - is one of the reactants in photosynthesis.
If the concentration of carbon dioxide is increased, the rate of photosynthesis will therefore increase.
Eventually the increase will plateau because another input, such as water or light, has become a limiting factor
How does Light effect photosynthesis
Without enough light, a plant cannot photosynthesise very quickly - even if there is plenty of water and carbon dioxide and a suitable temperature.
Increasing the light intensity increases the rate of photosynthesis , until some other factor - a limiting factor - becomes in short supply.
How does temperature effect photosynthesis?
The chemical reactions that combine carbon dioxide and water to produce glucose are controlled by enzymes. As with any other enzyme-controlled reaction, the rate of photosynthesis is affected by temperature.
At low temperatures, the rate of photosynthesis is limited by the number of molecular collisions between enzymes and substrates. At high temperatures, enzymes are denatured.
