5 Plasma membranes OCR Biology A Exam-style mark scheme

OCR Biology A

5 Plasma membranes Exam-style mark scheme

Question number

Answer

1 a

D cholesterol

E protein / glycoprotein

F phospholipid (head / bilayer)

1 b

D stabilised membrane / controls fluidity / reduces

permeability to charged particles

E allows, communication / transport of polar molecules

F acts as a barrier (to charged / polar molecules)

1 c

Any two from:

For communication between cells

For cell recognition / identification

For coordination of action of different cells

To trigger a response inside a cell

Marks B3

Guidance

B3

Reference to a hormone or drug binding is the communication idea. B2

2 a

Any two from:

B2

Active transport uses energy / ATP but facilitated diffusion does not

Active transport can move substances against a diffusion gradient (from low to high concentration) but in facilitated diffusion movement is always down the gradient (from high to low)

In active transport the carrier protein changes shape, but in facilitated diffusion it does not

2 b

Any two from:

B2

Bulk transport can move various soluble and insoluble substances but osmosis refers to movement of water only

Bulk transport can move substances against a diffusion gradient (from low to high concentration) but in osmosis movement is always down the water potential gradient (from high to low )

Bulk transport involves fusion or formation of vesicles at the cell surface membrane, changing its size, but osmosis does not

2 c

Proteins are intact at 20?C but denatured at 80?C

B2

Phospholipids form a stable bilayer at 20?C but move more and break apart making gaps in the membrane at

80?C

? Oxford University Press 2015 oxfordsecondary.co.uk/acknowledgements

This resource sheet may have been changed from the original

1

OCR Biology A

5 Plasma membranes Exam-style mark scheme

Question number

Answer

3 a i

Liver cell-surface membrane AND Golgi membrane

Have most carbohydrate / glycolipid / glycoprotein

3 a ii

Mitochondrion inner membrane

High protein content due to membrane-bound enzymes

3 a iii

Unicellular protoctist cell-surface membrane and mitochondrion outer membrane

Highest lipid / phospholipid content

3 b

Liver cell part of a multicellular organism so needs to

communicate / has more protein receptors

Protoctist proteins may detect chemicals in environment or act as channels

3 c

Protein ? C, H, O, N, S

(Phospho)lipid ? C, H, O, P

Carbohydrate ? C, H, O

4 a

0.0?1.0moldm-3

4 b

As sucrose concentration increases the number of

plasmolysed cells increases

Curve is a straight line showing positive correlation

Marks B2 B2 B2

B2

Guidance

B3

B1 A larger range, up to 2.0moldm-3, is acceptable. The units `M' should be corrected to moldm-3.

B1 M1

4 c

Read off sucrose solution that causes 50% plasmolysis

B2

(= incipient plasmolysis)

Use published table or graph to look up the water potential in kPa of this sucrose concentration

5 a

Working

magnification = size of image / size of real object

M2 Answers of ?2900 to ?3100 are acceptable.

= 30mm / 10m

= 30000 m / 10m

Answer = ?3000

5 b

Any four points from:

B4 Underlined words are

Water will enter by osmosis

essential, no alternatives allowed.

Down water potential gradient / from high to low

Because of cells is lower / more negative

Cells / vacuoles expand

Cell membrane presses against cell wall

? Oxford University Press 2015 oxfordsecondary.co.uk/acknowledgements

This resource sheet may have been changed from the original

2

OCR Biology A

5 Plasma membranes Exam-style mark scheme

Question number

Answer

increases until equilibrium

Cell wall resists expansion / prevents bursting

5 c i

Chloroplast

5 c ii

Any one from:

Creates separate compartment from cell for reactions

Controls what enters and exits (this compartment)

5 d

Any two from:

A takes up water (by osmosis)

Bursts

As membrane not strong enough / no cell wall

Marks

B1 B1

B2

Guidance

? Oxford University Press 2015 oxfordsecondary.co.uk/acknowledgements

This resource sheet may have been changed from the original

3

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