[B4] Bioenergetics

What is photosynthesis?

A reaction in plants where carbon dioxide and water react in the presence of light to form glucose and oxygen

Where does photosynthesis take place?

In chloroplasts in green plant cells

Where is the energy for photosynthesis taken from?

light radiation from the Sun

What type of reaction is photosynthesis?

Endothermic (energy is taken in from the surroundings)

What is the word equation for photosynthesis?

Carbon dioxide + water → glucose + oxygen

What is the symbol equation for photosynthesis?

6 CO₂ + 6 H₂O → C₆H₁₂O₆ + 6 O₂

What are the three main limiting factors of photosynthesis? (4)

Light intensity

CO₂ concentration

Temperature

Chlorophyll can also be a factor

How does temperature affect the rate of photosynthesis? (2)

If the temperature is low, the enzymes needed for photosynthesis work more slowly

If the plant gets too hot (around 45°C), the enzymes become damaged, so they can’t catalyse reactions

[𝐇𝐢𝐠𝐡𝐞𝐫] What is the relationship between rate of photosynthesis and light intensity?

rate of photosynthesis is directly proportional to light intensity

[𝐇𝐢𝐠𝐡𝐞𝐫] What is the relationship between light intensity and the distance from a light source?

light intensity is inversely proportional to the square of the distance to the source

[𝐇𝐢𝐠𝐡𝐞𝐫] How can greenhouses be used to get the maximum rate of photosynthesis while still maintaining profit? (2)

Greenhouses trap the sun's heat which increases temperature

There are also methods to increase CO₂, like burning paraffin

[𝐇𝐢𝐠𝐡𝐞𝐫] Give the law that links light intensity and distance. (2)

light intensity is inversely proportional to the square of the distance

light intensity = 1 ÷ d²

How do plants use glucose? (5)

respiration

converted into insoluble starch for storage

to produce fat or oil for storage

to produce cellulose, which strengthens the cell wall

to produce amino acids for protein synthesis

What is cellulose used for in plants?

Making strong cell walls

Why do plants store starch?

It is a source of stored energy ready for when photosynthesis isn't happening

Why do plants store energy as starch, rather than glucose?

Starch is insoluble, which is better for storing because it doesn't absorb water

What is respiration?

an exothermic reaction which is continuously occurring in living cells to provide energy for living processes

When does respiration occur in plants?

All the time

When is the rate of respiration greater than the rate of photosynthesis in plants?

When it is dark eg. at night

What happens when the rate of respiration is greater than the rate of photosynthesis in plants?

The carbon dioxide concentration increases

Is respiration exothermic or endothermic?

Exothermic

How do organisms use energy from respiration? (3)

Chemical reactions to build larger molecules

movement

keeping warm

What is aerobic respiration? (2)

Respiration using oxygen

It is the most efficient way to transfer energy from glucose

What is anaerobic respiration? (2)

Respiration without oxygen

It is the incomplete breakdown of glucose

Where does aerobic respiration happen?

in the mitochondria

Where does anaerobic respiration happen?

in the cytoplasm

What is the word equation for respiration?

Glucose + oxygen → carbon dioxide + water

What is the symbol equation for respiration?

C₆H₁₂O₆ + 6 O₂ → 6 CO₂ + 6 H₂O

What is the word equation for anaerobic respiration in humans?

Glucose → lactic acid

What is the word equation for anaerobic respiration in plants and yeast cells?

Glucose → ethanol + carbon dioxide

What is the name given to anaerobic respiration in yeast cells?

Fermentation

When do human body cells start to respire anaerobically?

When you do vigorous exercise and your body can't supply enough oxygen to your muscles

Why do human body cells start to respire anaerobically?

if your body can't supply enough oxygen to your muscles cells they start to anaerobically respire as well as aerobically

Why is anaerobic respiration undesirable? (2)

It doesn't transfer as much energy as aerobic respiration

It causes lactic acid to build up in the muscles, which is painful

How is fermentation used in industry? (2)

Bread making: the carbon dioxide released from fermentation makes bread rise

Making alcoholic drinks, e.g. beer because fermentation produces ethanol.

How does your body increase the amount of oxygen that gets to your cells when you exercise? (2)

Breathing rate and depth increases (to get more oxygenated blood to cells)

Heart rate increases (to get oxygenated blood to cells quicker, and to remove CO₂ quicker)

How could you measure breathing rate?

By counting the number of breaths taken in a certain period of time

How could you measure heart rate?

Counting the number of pulses on your wrist/neck in one minute

What happens to muscles after long periods of exercise? (2)

Muscle fatigue

muscles get tired and stop contracting efficiently

What is 'oxygen debt'? (2)

After cells have respired anaerobically, the body needs more oxygen

This is to react with the buildup of lactic acid to remove it from cells (forming CO₂ and water)

[𝐇𝐢𝐠𝐡𝐞𝐫] What happens to lactic acid to remove it from the muscles?

Blood flowing through the muscles transports the lactic acid to the liver where it is converted back into glucose

What is metabolism?

The sum of all the chemical reactions occuring in an organism.

Give examples of metabolic reactions (6)

Glucose ⇌ starch (plants)

Glucose → cellulose (plants)

Glucose ⇌ glycogen (animals)

Glycerol + 3 fatty acids ⇌ lipids

Glucose + nitrates ⇌ amino acids

Amino acids ⇌ proteins

What is the function of waxy cuticle?

Protective layer that prevents water from evaporating from the surface of the leaf

What is the function of the upper epidermis?

Thin and transparent to allow light to enter palisade mesophyll layer underneath it

What is the function of the palisade mesophyll?

Column shaped cells tightly packed with chloroplasts to absorb more light, maximising photosynthesis

What is the function of the spongy mesophyll?

Contains internal air spaces that increases the surface area to volume ratio for the diffusion of gases (mainly carbon dioxide)

What is the function of the lower epidermis?

Contains guard cells and stomata

What is the function of guard cells?

Absorbs and loses water to open and close the stomata to allow carbon dioxide to diffuse in, oxygen to diffuse out

What is the function of stomata? (3)

Where gas exchange takes place

Opens during the day, closes during the night, evaporation of water also takes places from here

In most plants, found in much greater concentration on the underside of the leaf to reduce water loss

What is the function of the vascular bundle?

Contains xylem and phloem to transport substances to and from the leaf

What is the function of xylem?

Transports water into the leaf for mesophyll cells to use in photosynthesis and for transpiration from stomata

What is the function of the phloem?

Transports sucrose and amino acids around the plant