Photosynthesis

The process that makes life of Earth possible

Chloroplasts

• Where Photosynthesis takes place• Holds many flat bag shaped membranes called

thylakoids– Thylakoid – collect light using chlorophyll– Connected to one another and arranged in stacks

called grana (stacks of pancakes)– Stroma (pancake syrup)- liquid filled space around

the thylakoids

Remember: - To make a large molecule (glucose) you need Energy

- When you break down a large molecule (glucose) yougenerate Energy

Photo (light)-synthesis (putting things together)

How do Plants get Water?

How do Plants get water?

• Water from the soil gets brought up from the roots to the leaves

• Water gets pulled up as water evaporates from leaves because of heat from the sun – think of how liquid gets from the bottom of a cup to your mouth with a straw

How do Plants get Carbon Dioxide?

How do plants get carbon dioxide?

• Stomata or tiny openings in the bottom of the leaf let carbon dioxide in and oxygen out

How do plants get light energy from the sun?

• We already know this! Plants trap light energy from the sun using the pigment chlorophyll which is found in the chloroplast

Now we have all 3 ingredients: ____________________________

Why is photosynthesis so important?

• All the energy on the planet comes from the sun• Autotrophs are the only organisms that can harness

that energy• All the energy for living things starts with the

autotrophs who capture it from the sun!• Every food chain starts with an autotroph and all the

energy in that food chain originated with the sun!!

2 Steps of Photosynthesis

1. Light-dependent reactions: convert the sun's energy into chemical energy - generate the energy needed for the next step

2. Light-independent reactions: use the energy from step 1. and Carbon dioxide to make glucose (food)

Step 1

• Occurs in two different areas of the thylakoid – Photosystem I and Photosystem II

• Photosystem – light collecting unit of the chloroplast

• Photosystem has Chlorophyll and Electron Transport Chain (a chain of Carrier Proteins)

Light electrons

- The more Energy an electron has , the further away from the protons it can get;

- Given enough energy it can escape altogether leaving behind a (+) charged particle – ion

- When an electron falls closer to protons, it releases energy

- When Hydrogen (picture) looses 1 electron, it becomes a H+ ion

Step 1 – getting that energy from the sun

• Light-dependent – reactions need light• Require water and sunlight• Chlorophyll absorbs the energy from the sun –

(high energy particles called photons) – with enough energy 2 electrons will pop off from chlorophyll

• To replace these lost electrons from Chlorophyll - photons will split water into oxygen, hydrogen ions and electrons – O2 H+ e-

Step 1 – Photosystem II

• The 2 electrons from Chlorophyll will travel down the electron transport chain (ETC) – a chain of carrier proteins

• Each time the electrons jump from 1 carrier protein to another they will release some energy

• The energy from the electrons is then used to transport H+ across the membrane – result high concentration of H+ inside the thylakoid

ATP formation

• H+ ions build up inside the thylakoid• H+ wants to move from high to low

concentration (Diffusion) but it needs help from a protein in the cell membrane called ATP synthetase (channel protein + enzyme)

• As H+ passes through, ATP synthetase is forced to turn and when it does it adds a phosphate group to ADP to make ATP

Step 1 – Photosystem I

The electrons from photosystem II lost energy when they pumped H+ across the membrane

In photosystem I light gives the electrons energy again

Then they go through another ETC Here they are used to make NADPH which go

on to the next set of reactions

Summary of Light dependent reactions• Require water and sunlight, have 2 parts:

photosystem II and photosystem I• As light shines on Chlorophyll it looses 2

electrons, and replaces them with 2 electrons from water

• As the plant uses the electrons from water H+ and O2 are left behind

• Oxygen gas is given off in photosystem II and ATP is made

• NADPH is made in photosystem I

Step 2 – Light-independent reactions

• Also called Dark reactions or the Calvin cycle• Takes place in the stroma of the chloroplast• Need carbon dioxide to build carbohydrates• Use hydrogen, ATP and NADPH (energy) from

light dependent reactions and carbon dioxide to make carbohydrates/glucose

Dark Side of Photosynthesis

To be Continued.............

Step 2 - Light-Independent Reactions........

Glucose

.........Also known as The Calvin cycle

From Step 1 – Light-dependentReactions

From Air by way of Stomata

The Calvin Cycle

• Called a cycle because the starting material is regenerated each time the process occurs

• Enzymes join carbon dioxide molecules with molecules that are already in the cell - these molecules will regenerate each time

• The energy from ATP and NADPH are used in this process

3 X 5-C molecules ( 15 C) + 3 CO2

6 x 3-C molecules (18 C)

1X 3-Cmolecule

5 x 3-C molecules

product/leaves the cycle2 of these make 1 glucose

Sugar ProductionWith each turn of the Calvin cycle a few 3C

sugars leave the cycle

These molecules become the building blocks that the plant cell uses to make sugars, lipids, amino acids and other compounds

The plant will use these compounds as the food and building materials it needs to grow

Summary of Light Independent Reactions

Calvin cycle uses ATP and NADPH from light dependent reactions and carbon dioxide from the air to make sugars

Plant uses the sugar to meet its energy needs and to build molecules needed for growth

When other living things eat these plants they too will get the energy they need.

Factors that Affect Photosynthesis• The process can speed up or slow down

depending on several factors• Temperature: enzymes work best between 15-

35 degrees Celsius• Light: very bright light speeds up

photosynthesis• Water levels

Water Loss and Photosynthesis

• Water is lost through the stomata where carbon dioxide enters

• If its hot the plants will close the stomata to keep from loosing water but photosynthesis will slow down due to the lack of carbon dioxide

• Some plants that live in dry areas have special ways to save water and carry out photosynthesis

C4 Plants

• Have a special chemical pathway that gets carbon dioxide into the Calvin cycle

• It uses extra ATP but it allows the plant to carry out photosynthesis when its hot

• Examples: Corn, sugar cane

CAM Plants

• Save water by taking air into their leaves only at night

• At night carbon dioxide is used to make acids• During the day these acids are turned back

into carbon dioxide for photosynthesis• Example: Pineapples trees, desert cacti