5.6.2: Chloroplasts and photosynthetic pigments Flashcards Preview

Biology A2: 5.6 > 5.6.2: Chloroplasts and photosynthetic pigments > Flashcards

Flashcards in 5.6.2: Chloroplasts and photosynthetic pigments Deck (25)
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1
Q

What are chloroplasts and where are they found?

A
  • The organelles in plants where photosynthesis takes place.
  • Algae have chloroplasts but photosynthetic bacteria do not.
2
Q

Describe the structure and permeability of chloroplasts.

A
  • Disc shaped
  • Around 2-10 um long
  • Each surrounded by a double membrane, the envelope with an intermembrane space of width 10-20um between the inner and outer membrane.
  • The outer membrane is highly permeable.
3
Q

What are the two distinct regions, visible on electron micrographs, inside a chloroplast?

A
  • The fluid-filled matrix called the stroma

- The grana consisting of stacks of thylakoid membranes.

4
Q

Where does the first stage of photosynthesis, the light-dependent stage take place?

A

In the grana.

5
Q

What are the three distinct membranes in chloroplasts and what are the three internal compartments that they form?

A
  • Outer
  • Inner
  • Thylakoid
    giving. ..
  • Intermembrane space
  • stroma
  • Thykaloid space
6
Q

How are thykaloids within a granum connected to thykaloids within another granum?

A

By intergranal lamellae (or intergranal thykaloids)

7
Q

What is a thykaloid?

A

Flattened membrane-bound sac found inside chloroplasts; containing photosynthetic pigments/photosystems and is the site of the light-dependent stage of photosynthesis.

8
Q

What are stacks of thykaloids called?

A
  • A granum (may contain 100 thykaloids)

- Plural, grana

9
Q

What is the benefit of having many grana in every chloroplast and many chloroplasts in each photosynthetic cell?

A

Huge surface area for:

  • The distribution of photosystems that contain the photosynthetic pigments that trap sunlight energy.
  • Electron carriers and ATP synthase enzymes needed to convert light energy to ATP.
10
Q

What holds the photosystems in place?

A

Proteins embedded into the thykaloid membrane.

11
Q

What is the benefit of having the grana surrounded by the stroma?

A

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

12
Q

What is the stroma and what does it contain?

A
-The fluid filled matrix. 
Contains: 
-enzymes needed to catalyse the reactions of the light-independent stage of photosynthesis. 
-Starch grains
-Oil droplets 
-Small ribosomes 
-DNA
13
Q

What does the loop of DNA in chloroplasts contain?

A
  • genes that code for some of the proteins needed for photosynthesis.
  • These proteins are assembled at the chloroplast ribosomes.
14
Q

Where are photosytems found and what do they contain?

A
  • Within the thykaloid membrane are funnel shaped structures called photosystems.
  • They contain photosynthetic pigments.
15
Q

Why is there a need for a variety of photosynthetic pigments?

A

-Each pigment absorbs light at of a particular wavelength and reflects other wavelengths of light.

16
Q

How does a photosystem work?

A

-The energy associated with the wavelengths of light captured is funnelled down to the primary pigment reaction centre, consisting of a type of chloryphyll, at the base of the photosystem.

17
Q

What are chlorophylls?

A
  • A mixture of pigments.
  • All have a similar molecular structure consisting of a porphyrin group, in which there is a magnesium atom and a long hydrocarbon chain.
18
Q

There are two forms of chlorophyll a. In which ways are they the same?

A
  • Both appear blue-green
  • Both situated at the centre of photosystems
  • Both absorb red light
19
Q

What is different about the two forms of chlorophyll a?

A

They have different absorption peaks.

20
Q

Where is P680 found and which wavelength of light is its peak of absorption?

A
  • Photosystem II

- wavelength 680 nm

21
Q

Where is P700 found and which wavelength of light is its peak of absorption?

A
  • Photosystem I

- wavelength 700nm

22
Q

Which wavelength of light does chlorophyll a also absorb (not 680 nm and 700 nm)?

A

-Some blue light of wavelength around 440 nm.

23
Q

Which wavelengths of light does chlorophyll b absorb?

A

400-500 nm and 640 nm.

-It appears yellow green.

24
Q

Which wavelengths of light do carotenoids absorb and reflect?

A
  • Blue light if wavelengths 400-500 nm

- They reflect yellow and orange light.

25
Q

Which wavelengths of light do xanthophylls absorb and reflect?

A
  • Blue and green light if wavelengths 375-550 nm

- They reflect yellow light.