5.6 - Photosynthesis

Question 1

What is autotrophic nutrition?

Answer 1

Type of nutrition where organic molecules are synthesised from inorganic molecules such as carbon dioxide and water.

E.g. photosynthesis where sunlight energy is converted to chemical energy = used to synthesise large organic molecules from small inorganic molecules.

Question 2

What are two names for organisms at the beginning of the food chain and why do they have these names?

Answer 2

PHOTOAUTOTROPHS: Organisms that photosynthesise.
- because they use light as the energy source for autotrophic nutrition.

PRODUCERS:
They are at the beginning (first trophic level) of a good chain.
- provide energy & organic molecules to other, non-synthetic, organisms.

Question 3

Give the general equation for photosynthesis:

Answer 3

6CO2 + 6H2O —> (chlorophyll)

C6H12O6 + 6O2

Question 4

What is a photon?

Answer 4

A particle of light; each photon contains an amount (a quantum) of energy.

Question 5

Why is photosynthesis an example of carbon fixation?

Answer 5

Because it is a process by which carbon dioxide is converted into sugars.

Question 6

What kind of reaction is carbon fixation? (Two details)

Answer 6

• an endothermic reaction = requires energy

- a reduction reaction = needs electrons

Question 7

Why is carbon fixation useful?

Answer 7

• helps regulate the concentration of carbon dioxide in the atmosphere and oceans.

Question 8

Why is photosynthesis important to all organisms not just plants?

Answer 8

• most forms of life on Earth rely directly or indirectly on photosynthesis.

Question 9

Why do plants need energy?

Answer 9

They need energy for things like photosynthesis, active transport, DNA replication, cell division and protein synthesis.

Question 10

Who do animals need energy?

Answer 10

Animals need energy for things like muscle contraction, maintenance of body temp., active transport, DNA replication, cell division & protein synthesis.

Question 11

How do plants respire?

Answer 11

They oxidise the organic molecules that they have previously synthesised by photosynthesis & stored, releasing chemical energy.

Question 12

How do non-photosynthetic animals respire?

Answer 12

Non-synthetic organisms are organisms that cannot photosynthesise.

• they consume food
• they obtain energy from the products of digestion by respiration.

Question 13

What happens in respiration?

Answer 13

Glucose and other organic compounds are oxidised to produce carbon dioxide and water.

Question 14

Is respiration endo or exothermic?

Answer 14

Respiration is exothermic.

- releases chemical energy that can drive the organism’s metabolism.

Question 15

Give the formula for respiration.

Answer 15

C6H12O6 + 6O2 → 6CO2 + 6H2O (glucose + oxygen -> carbon dioxide + water)

Question 16

Give the two types of respiration.

Answer 16

Aerobic respiration:
- using oxygen

Anaerobic respiration:
- without oxygen

Question 17

Metabolic pathway definition:

Answer 17

a series of small reactions controlled by enzymes, e.g. respiration and photosynthesis

Question 18

Phosphorylation definition:

Answer 18

adding phosphate to a molecule e.g. ADP is phosphorylated to ATP

Question 19

Photophosphorylation definition:

Answer 19

adding phosphate to a molecule using light

Question 20

Photolysis definition:

Answer 20

the splitting (lysis) or a molecule using light (photo) energy

Question 21

Hydrolysis definition:

Answer 21

the splitting (lysis) of a molecule using water (hydro)

Question 22

Decarboxylation definition:

Answer 22

• the removal of carbon dioxide from a molecule

Question 23

Dehydrogenation definition:

Answer 23

the removal of hydrogen from a molecule.

Question 24

Redox reaction definition:

Answer 24

a reaction that involves oxidation and reduction

Question 25

When do plants photosynthesise and why?

Answer 25

Plants only photosynthesise during the day.

Question 26

What is the term to describe when photosynthesis and respiration proceed at the same rate?

Answer 26

The plant is at its compensation point.

Question 27

The time a plant takes to reach its compensation point is called the ……?

Answer 27

Compensation period.

Question 28

Is the compensation period the same for all plant species?

Answer 28

No.

- the compensation period is different for different plant species.

Question 29

Describe the difference in response between a shade plant and a sun plant when they are both exposed to light.

Answer 29

SHADE PLANTS:
- can utilise light of a lower light intensity that sun plants can.
- when exposed to light after darkness, shade plants reach their compensation point sooner
> have a shorter compensation point than sun plants.

SUN PLANTS:
- require a higher light intensity to achieve their optimum rate of photosynthesis.

Question 30

What shape and how big are most chloroplasts?

Answer 30

• most plant chloroplasts are DISC SHAPED

- around 2-10μm long.

Question 31

Describe the basic structure of chloroplasts.

Answer 31

> each chloroplast is surrounded by a double membrane, the envelope, with an inter membrane space of width 10-20nm between the inner & outer membrane

> outer membrane = HIGHLY PERMEABLE.

> the stroma = the fluid filled matrix

> grana = consist of stacks of thylakoids membranes

Question 32

Where does the first stage of photosynthesis take place and what is this stage called?

Answer 32

The grana

- it is called the light-dependent stage.

Question 33

How many membranes do chloroplasts have?

Answer 33

3. • the outer, inner and thylakoid
     Gives three separate internal compartments:
     > the intermembrane space
     > the stroma
     > the thylakoid space

Question 34

Is the thylakoid membrane of each chloroplast highly permeable or slightly permeable?

Answer 34

Not very permeable.

Question 35

Why is useful that the grana are so small and there are many chloroplasts within each cell?

Answer 35

It means there is a huge surface area for:

• the distribution of the photosystems that contain the photosynthetic pigments that trap sunlight energy
• the electron carriers and ATP synthase enzymes needed to convert that light energy into ATP.

Question 36

Why is important that there are proteins embedded in the thylakoid membranes?

Answer 36

So the photosystems are held in place.

Question 37

Why are the grana surrounded by stroma?

Answer 37

So the products of the light-dependent stage can easily pass to the stroma to be used in the light-independent stage.

Question 38

What does the stroma contain?

Answer 38

Contains the enzymes needed to catalyse the reactions of the light-independent stage of photosynthesis, as well as:
> starch grains
> oil droplets
> small ribosomes similar to those found in prokaryote cells

Question 39

What does the loop of DNA in the stroma contain?

Answer 39

Genes that code for some of the proteins needed for photosynthesis.
- these proteins are assembled at the chloroplast ribosomes.