Biology: Autotrophs and Heterotrophs, Plant Organization and Photosynthesis

Study Notes

Autotrophs produce their own food, using energy from the environment, whereas heterotrophs obtain energy by consuming other organisms.
Photoautotrophs, such as plants, receive energy from the sun.

Leaves are the primary site of photosynthesis in plants, and are often flat and broad to maximize sunlight absorption.
The middle layer of the leaf, called the mesophyll, is where photosynthesis occurs, and contains cells surrounded by air spaces.
Stomata in the epidermis allow for gas exchange between the mesophyll cells and the surrounding air.
Chloroplasts, organelles within mesophyll cells, are the site of photosynthesis.
Thylakoids, stacked, disc-shaped membranes within chloroplasts, contain the photosynthetic pigment chlorophyll.

There is an inverse relationship between energy and wavelength of electromagnetic radiation, meaning shorter wavelengths have more energy.
The order of visible light colours from highest to lowest energy is: Violet → Blue → Green → Yellow → Orange → Red.

Chlorophyll a absorbs wavelengths in the red, orange, blue, and violet sections of visible light.
Green and yellow wavelengths are not absorbed, resulting in their reflection and transmission, giving plants their characteristic green colour.

A photon of light energy is absorbed by a pigment molecule in Photosystem II, exciting an electron.
The electron breaks free, and water is split to replace it, releasing oxygen.
The electron is passed through a series of pigment molecules, ultimately reaching the primary electron acceptor.
The electron is then transferred to the electron transport chain, pumping hydrogen ions from the stroma to the thylakoid space.
The electron is passed to Photosystem I, where another photon of light is used to energize an electron.
The electron is then passed to a protein that uses the energy to produce NADPH.
The pumping of hydrogen ions allows for the production of ATP through the protein ATP synthase.