Intro to Photosynthesis

Green Book – 4.2 and 4.3Blue Book – Chapter 6

Reviewing Why We Need Photosynthesis

• Photosynthesis is the process that feeds the biosphere.

• Photosynthesis feeds the entire world either directly or indirectly.

• Sun -> Autotrophs (producers) -> Heterotrophs (consumers and decomposers)

Plant Anatomy

• All green parts of the plant, including stems, contain organelles called chloroplasts.

• Chloroplasts get their color from a pigment called chlorophyll.• There are about a half million chloroplasts per square millimeter

of leaf surface.• Most chloroplasts are located in the mesophyll, the tissue in the

interior of the leaf.– Mesophyll cells each contains 30-40 chloroplasts

• Gas exchange happens through a structure in the leaf surface called stomata. – Carbon dioxide enters– Oxygen exits

Chloroplasts

• All green parts of the plant, including stems, contain organelles called chloroplasts.– A double membrane encloses each chloroplast, keeping

the stroma (dense fluid that fills each chloroplast, sort of like cytoplasm) contained.

– A mass of interconnected membranes, called thylakoids, are housed inside the chloroplasts and are surrounded by stroma. This is where chlorophyll is strored.

– Sometimes, thylakoids are found in stacks. These stacks are called grana.

What Happens on a Molecular Level?

6 CO2 + 6 H2O + Light Energy -> C6H12O6 + 6 O2

Two Stages of Photosynthesis

• There are two stages of photosynthesis:– Light Reactions– The Calvin Cycle

Light Reactions

• Light reactions are the steps of photosynthesis that convert solar energy to chemical energy.– Chlorophyll absorbs energy from the sun. – Energy is transferred across the thylakoid

membranes through the splitting of water.– Oxygen is released.– Energy is transferred to ATP.

Light Independent Reactions(Calvin Cycle)

• ATP from the light reactions is used to make sugar. This occurs in the stroma of the chloroplasts.– CO2 is added to make bigger molecules.– A molecule of glucose is formed and is used to

store energy.

Crash Course - Photosynthesis

• https://www.khanacademy.org/partner-content/crash-course1/partner-topic-crash-course-bio-ecology/crash-course-biology/v/crash-course-biology-108