2.5 ultrastructure of plant cells

Question 1

Describe cell walls

Answer 1

Plant cell walls are made of cellulose, a complex carbohydrate. Freely permeable so substances can pass into and out of the cell through the cellulose wall. The contents of the cell press against the wall making it rigid.

Question 2

Purpose of cell walls

Answer 2

Gives the cell shape. It supports both the individual cell and the whole plant. The cell wall also acts as a defence mechanism, protecting the contents of the cell against invading pathogens.

Question 3

What are vacuoles?

Answer 3

Vacuoles are membrane lined sacs in the cytoplasm containing cell sap. The membrane is called the tonoplast.

Question 4

Role of vacuoles

Answer 4

Large permanent vacuoles are important in the maintenance of turgor, so that the contents of the cell push against the cell wall + maintain a rigid framework. Selectively permeable.

Question 5

Can vacuoles be present in animal cells?

Answer 5

Yes, but if they do appear, they are small and transient (not permanent).

Question 6

What are chloroplasts?

Answer 6

The organelles responsible for photosynthesis.

Question 7

Structure of chloroplasts

Answer 7

Have a double membrane structure. The fluid enclosed is called the stroma. Have an internal network of membranes, which form flattened sacs called thylakoids. Several thylakoids stacked together are called a granum. Starch produced is present in starch grains.

Question 8

Describe grana

Answer 8

Grana are joined by membranes called lamellae. They contain chlorophyll pigments, where light-dependent reactions occur.

Question 9

What else do chloroplasts contain?

Answer 9

DNA and ribosomes, thus chloroplasts are able to make their own proteins.