Bioenergetics - 4.4

Photosynthesis

An endothermic reaction in which plants use light energy to convert carbon dioxide and water into glucose and oxygen.

Where does photosynthesis happen?

• Takes place in chloroplasts in green plant cells

• Contains pigments like chlorophyll that absorb light

How does photosynthesis get its reactants and what does it do with the products?

• CO2 enters the leaf from the air via diffusion

• Water reach the cells via the xylem

• Oxygen is released as a by product

• Glucose is used in the plant

Word Equation for Photosynthesis

Carbon dioxide + Water LIGHT —> Glucose + Oxygen

Symbol Equation for Photosynthesis

6CO₂ + 6H₂0 LIGHT —> C₆H₁₂O₆ + 6O₂

What is glucose used for in plants?

• Respiration

• Cellulose

• Amino Acids

• Lipids

• Starch

Respiration - Glucose

They break down the glucose to release energy

Cellulose - Glucose

Used to make cellulose to make strong cell walls

Amino Acids - Glucose

Combined with nitrate ions to make amino acids which eventually create proteins.

Lipids - Glucose

Convert the glucose into fats and oils that server as energy storage. eg. Seeds

Starch - Glucose

Used to store glucose for a later time. It is useful because it is compact,insoluble and easy to break down when needed.

Limting Factors Of Photosynthesis

• Chlorophyll Concentration

• Light Intensity

• Carbon Dioxide Concentration

• Temperature

Chlorophyll Concentration and affect on photosynthesis

• These is not enough chlorophyll in the plant to absorb the light

• This could be because of infection (TMV) , Environmental stress and lack of nutrients

Light Intensity

• Rate increases with light intensity up to a certain point

• Light Intensity was the limiting factor as there was not enough energy so increasing it increases the rate

• The graph then plateaus

• This is because there is a different limting factor such as CO2 or temperature

Carbon Dioxide Concentration

• Rate increases with CO2 Conc up to a certain point

• CO2 conc was the limiting factor as there was not enough as it is a reactant so increasing it increases the rate

• The graph then plateaus

• This is because there is a different limiting factor such as light intensity or temp

Temperature

• Rate increases with temperature as enzymes can work quicker

• This is because the particles have more energy and move faster so they react more frequently

• Highest rate is at optimum temperature for enzyme

• At high temp the rate decreases as bonds holding the enzyme together begin to break, and so the enzyme changes shape

• Rate falls to zero as enzymes denature

More than one Limiting Factor

• Both lines show that as light intensity increases so does the rate

• However the line then plateaus as temperature becomes the limiting factor

• The line with the higher temp has a higher max rate of photosynthesis as it started to limit later on

How can farmers keep plants conditions ideal?

• Temperature

• Artificial Light

• CO2 Concentration

• General health of plants

Temperature - Plant Conditions

• Greenhouses help to trap the suns heat and makes sure temp doesn’t become limiting

Light - Plant Conditions

• When the sun goes down or when it isn’t bright enough farmers can supply the plants with artificial light for more photosynthesis time

CO2 Concentration + Temperature - Plant Conditions

• Farmers can use paraffin burns to heat the greenhouse so temperature is not a limiting factor and it makes CO2 as a by product so CO2 conc is not a limiting factor.

General Health - Plant Conditions

• Keeping plants enclosed in a greenhouse helps them to stay away from pests and diseases

• Farmers can add fertiliser to the soil to provide minerals for growth

Greenhouse Costs?

• Farmers only use greenhouses to improve condition so the plant grows faster/get a better yield

• However it is expensive so it must be worth it

• No need to supply stuff it does not need as that will be a waste of money

Variables for Photosynthesis Practical

• IV: Light Intensity

• DV: Amount of Oxygen produced

• CV: CO2 Conc,Temperature,Size/Type of Pondweed (different chlorophyll quantity)

Inverse Square Law

light intensity = 1/distance ² (inversely proportional)

Resipration

An exothermic reaction which releases energy from glucose and continuously occurs in living cells

Aerobic Respiration

• Starts in the cytoplasm and occurs in the mitochondria

• Uses oxygen to release energy from glucose molecules (by oxidising it)

Aerobic Respiration Word Equation

Glucose + Oxygen —> Carbon Dioxide + Water

Aerobic Respiration Symbol Equation

C₆H₁₂O₆ + 6O₂ —> 6CO₂ + 6H₂O

Uses of Energy

• Build up larger molecules from smaller ones (proteins to amino acids)

• Allows for their muscles to contract

• Mammals and Birds use energy to keep their body temp steady

Anaerobic Respiration

• Only in the cytoplasm

• Releases energy from glucose molecules without oxygen

Anaerobic Respiration Word Equation in Animals

Glucose —> Lactic Acid

Anaerobic Respiration Symbol Equation in Animals

C6H12O6 —> 2C3H6O3

Anaerobic Respiration Word Equation in Plants

Glucose —> Ethanol + Carbon Dioxide

Anaerobic Respiration Symbol Equation in Plants

C6H12O6 —> 2C2H5OH + 2CO2

Oxygen Debt

Amount of extra oxygen the body needs after excercise to react with the build-up of latic acid and remove it from the cells.

Fermentation

• Anaerobic Respiration in yeast cells

• CO2 from fermentation makes the bread rise

• Fermentation is the process the produces alcohol

Compare Aerobic and Anaerobic

1. Aerobic with O2 / Anaerobic without 

2. Aerobic produces CO2 and H2O / Anaerobic produces lactic acid / ethanol 

3. Anaerobic respiration quicker THAN aerobic 

4. Aerobic releases more energy THAN anaerobic 

5. Aerobic occurs in cytoplasm + mitochondria / Anaerobic occurs in cytoplasm only

Changes that happen to body after excercise

1. Heart rate increases BECAUSE pumps more blood / oxygen / glucose 

2. Breathing rate increases BECAUSE more O2 in

3. Breathing rate increases BECAUSE more CO2 removed 

4. Blood vessels dilate BECAUSE more blood to cells

5. Rate of AEROBIC respiration increases BECAUSE more energy released 

6. Temperature increases BECAUSE respiration is exothermic / energy released to surroundings 

7. More energy released to contract muscles 

What does liver do with latic acid?

The liver oxidises lactic acid into carbon dioxide and water, or converts it back into glucose to be used for energy or stored as glycogen.

Metabolism

• Metabolism is the sum of all the chemical reactions that happen in a cell or in the body

• Controlled by enzymes

Metabolic Reaction that Occur in:

Both:

• Respiration 

• Formation and breakdown of lipids into  3 x fatty acids and glycerol

• Formation of proteins  from amino acids

Animals:

• Formation of glycogen 

• Breakdown of excess proteins to urea 

Plants:

• Photosynthesis 

• Formation of starch 

• Formation of cellulose

• Combining nitrates with glucose to form amino acids