Cells

Describe the structure of the nucleus. (4 marks)

Describe the structure of the nucleus. (4 marks)

• Nuclear envelope

• Nuclear pores

• Chromosomes/chromatin

• Nucleolus

What are the functions of the nucleus? (2 marks)

• Codes genetic information to code for polypeptides

• Site of DNA replication

Name the structures labelled W to Z in the diagram (2 marks)

W - (cell surface) membrane
X - cell wall
Y - capsule
Z - flagellum

Outline the sequence of events following the production of extracellular proteins that leads to their release from the cell. (3 marks)

• Proteins move to Golgi apparatus where they are processed or modified

• Packaged into vesicles

• Vesicles moved to CSM where they fuse in a process called exocytosis

The epithelial cells of the small intestine have large numbers of mitochondria. Explain how this is an adaption for the function of these cells. (3 marks)

• Mitochondria is site of ATP production

• High respiration rate if there are lots of them for active transport.

• Energy released needed for the absorption of digested foods

Describe how he could make a temporary mount of a piece of plant tissue to observe the number of chloroplasts in the cells when using an optical microscope. (4 marks)

• Add a drop of water to the glass slide

• Obtain a thin section of plant tissue and place on slide

• Stain with iodine in potassium iodide

• Lower cover slip using a mounted needle

Describe and explain how cell fractionation and ultracentrifugation can be used to isolate mitochondria from a suspension of animal cells. (5 marks)

• Cell homogenisation to break open cells

• Filter to remove large debris and whole cells

• Use isotonic solution to prevent damage to organelles

• Keep cold to prevent damage by enzymes/use buffer to prevent protein denaturation

• Centrifuge (at lower speed) to separate nuclei/heavy organelles

• Re-spin supernatant at higher speed to get mitochondria in pellet

A scientist investigated the rate of absorption at different amino acid concentrations by cells lining the small intestine.

Use your knowledge of membrane transport to describe and explain the shape of the curve shown above. (4 marks)

• As the amino acid concentration increases, the rate of uptake increases

• Because as amino acid concentration increases, more amino acids move through carrier proteins

• The rate of uptake levels off at higher amino acid concentrations

• Because all carrier proteins are saturated

Use the graph to explain how this monoglyceride is transported into cells within the digestive system. (3 marks)

• Rate of uptake is proportional to concentration

• This means that monoglycerides move by simple diffusion

• Because they are lipid soluble

The student carried out several repeats at each ____________ . Explain why the repeats are important. (2 marks)

• Allows anomalies to be identified, which can then be ignored

• Makes the average more reliable

The sports drink contains sodium chloride. Sodium chloride increases uptake of glucose in the small intestine. Explain how. (4 marks)

• Sodium ions and glucose absorbed by co-transport

• Via channel proteins

• Sodium ions removed by active transport into blood

• Sodium ions enter epithelial cells by facilitated diffusion taking glucose with them

• Glucose moved by facilitated diffusion into blood

The diagram shows one of the test tubes from the 20°C water bath and one from the 65°C water bath.

What conclusion can be made about the effect of temperature on the damage to beetroot cells? Provide an explanation for your conclusion. (4 marks)

• water at 20°C caused no damage

  • to the cell-surface/plasma membrane

• 65°C caused damage to the membrane

• 65°C denatured membrane proteins OR 65°C increased fluidity/permeability of the membrane

Endocytosis and exocytosis are processes that move large molecules into and out of cells. 

Describe the similarities and differences between endocytosis and exocytosis. (3 marks)

• Both processes form vesicles

• Both processes require energy from ATP

• Endocytosis involves substances entering cell while exocytosis

Individuals that suffer with lactose intolerance cannot break down lactose and so it remains in the lumen of the intestine.

The presence of lactose decreases the volume of water that is absorbed into the blood, causing diarrhoea. 

Explain why undigested lactose in the intestine causes diarrhoea. (3 marks)

• lactose lowers the water potential (in the lumen of the intestine)

• this reduces the water potential gradient (between the intestine and blood)

• less water is reabsorbed into the blood by osmosis (from the intestine), so more water is present in faeces

Applying salt to a wound can help prevent bacterial infection.

Using your understanding of water potential, propose how the application of salt to a wound could eliminate bacteria. (3 marks)

• salt lowers the water potential of the solution surrounding the bacteria

• the bacterial cytoplasm contains a higher water potential than its surroundings

• water moves out the bacterial cells by osmosis

• loss of water from bacterial cells causes dehydration and death of bacteria

Explain the differences between facilitated diffusion and active transport. (3 marks)

• facilitated diffusion involves channel or carrier proteins while active transport only involves carrier proteins

• facilitated diffusion is passive while active transport is not passive

• facilitated diffusion takes place down/along a concentration gradient while active transport can occur up/against a concentration gradient