Photosynthesis 🍃 🌱

Photosynthesis:

The way in which plants make their own food using light.

Plants are...

autotrophs

Is photosynthesis anabolic or catabolic?

anabolic

Aim of photosythesis:

To get plant to make food.

How is light absorbed in photosynthesis?

Chlorophyll in the leaf

Chemical equation for photosynthesis:

reactents of photosynthesis

• carbon dioxide

• water

• light

products of photosynthesis:

glucose and oxygen

Where does Co2 come from in photosynthesis?

through stomata from atmosphere.

Where does water come from in photosynthesis?

Through roots - osmosis.

Where does light come from in photosynthesis:

• Sun

• Artificial light - lamps ect.

What impacts the rate of photosynthesis?

• Temperature (Enzymes)

• Light intensity

• CO2 levels.

Effect of increasing light intensity in greenhouse on plants:

• Supplies more light which stimulates plant crop growth.

• This increasing growth rate for plants

Effect of adding artificial CO2 to a greenhouse on plants:

• Supplies more carbon atoms to the dark stage of photosynthesis for glucose formation.

Effect of increasing tempeture of greenhouse on plants

• Increases rate of photosynthesis as it increases enzyme activity

ADP means...

adenosine diphosphate

What is ADP?

Low energy molecule made from adenosine & 2 phosphates.

Adenosine --- Phosphate --- phosphate

How to from ATP?

Add one phosphate to ADP.

Adenosine --- phosphate --- phosphate + phosphate

Adding a phosphate =

Phosphorylation

ATP stands for...

adenosine triphosphate

Stage 1 of photosynthesis =

The light stage ( Cyclic phosphorylation )

Why is the light stage called 'the light stage' ???

As it requires light.

The light stage ( Cyclic phosphorylation ) - Summary

• Light energy is absorbed by chlorophyll molecules = high energy.

• High energy electrons leave chlorophyll.

• They are passed through electron acceptors & lose energy.

• This energy is combines with ADP + P to form ATP & h20.

• Low energy electrons return to chlorophyll.

Why is it referred to as cyclic phosphorylation?

As electrons return to the chlorophyll at the end (Low energy)

Products formed in the light stage & their FATE:

• ATP - used in dark stage.

• H20 - Used in photolysis OR Lost via stomata in transpiration.

Why is oxygen a waste product of the light stage?

As it is not needed for the light stage to occur.

Pathway 2 of the light stage of photosynthesis:

Non cyclic phosphorylation.

The light stage ( Non - Cyclic phosphorylation ) - Summary

• High energy electrons leave the chlorophyll.

• As they move through electron acceptors...energy is lot so ADP + P = ATP.

• Photolysis occurs (split water) so O2, 4e- & 4e+ produced.

• NADP+ + 2e- = NADP - + H+ = NADPH.

• electrons return to the chloroplast from the water and thus the cycle begins again.

• Oxygen is used in respiration or released as waste

Why is it referred to as non cyclic phosphorylation?

As electrons does not return to chlorophyll.

Products formed During light stage:

• NADPH - Supplies protons & electrons for dark stage.

• ATP - Supplies energy for dark stage.

• Oxygen - used for respiration or released into the atmosphere.

Fate of high energy electrons:

• Used to make NADPH.

• Return to chlorophyll.

Two functions of NADPH:

1. Supply electrons.

2. Supply protons.

What is the source of protons (+) to make NADPH?

Photolysis (4e +)

Name another molecule other than chlorophyll that provides electrons in photosynthesis.

H20.

Photolysis:

The splitting of water using light energy during photosynthesis.

= O2, 4e- & 4e+.

Why is good that chlorophyll contains many chemicals?

Can absorb more energy

The role of Stomata in Photosynthesis:

Allows CO2 into plant which is required for photosynthesis

What is the fate of the end products of the dark stage?

Return to light stage.

Functions of glucose:

• Food for plant

• Respiration

Name the stage of photosynthesis controlled by enzymes:

The dark stage!!!

Investigating the effect of light intensity on the rate of photosynthesis: Method

• Cut stem of Elodea & attach a paperclip to the top of it to keep the plant submerged in the water.

• Switch off all lights & close blinds in room.

• place a small amount of hydrogen sodium carbonate into a test tube & fill it 3/4 of the way with distilled water.

• Place the Elodea into the test tube & place it in water bath at 25 degrees.

• Use metre stick to place the apparatus 1m from the fluorescent lamp.

• Allow the Elodea to adjust to its new light intensity for 5 mins.

• When adjusted, count number of bubbles coming from the stem for 1 min.

• Repeat this 3 times & get the average.

• Repeat steps 6-8, moving the apparatus 20cm closer to the lamp each hime.

• Form graph of results.

Why was Elodea used?

As its a green aquatic plant that can produce bubbles under water.

Why was sodium hydrogen carbonate used?

To maintain CO2 levels.

Water Bath @ 25 degrees =

Optimum temperature for enzyme activity.

What factor was kept constant?

CO2 levels - Using Sodium hydrogen carbonate.

What factor was varied?

Light intensity - Used metre stick & moved lamp a set distance closer to the plant each time & counted bubbles for 1 min.

Explain the shape of the graph that was drawn up:

• As light intensity increases...so does the number of bubbles.

• Graph levels off after reaches saturation point.

• This tells us that photosynthesis rate increases with light intensity until reaches saturation point.

What does saturation point mean?

Point where plant cannot photosynthesize any faster.

Importance of eliminating external light (Turn off lights, close blinds ect.)

• To ensure amount of bubbles produced is accurate due to the variable, eg change in light intensity by scientist.

X and Y axis of graph for rate of photosynthesis light intensity experiment...

X = light intensity

Y = rate

Role of NADPH in dark stage:

Transfer protons & electrons. CO2 is reduced to glucose.