2.5 The ultrastructure of plant cells

Question 1

What is the cellulose cell wall?

Answer 1

Surrounds the plasma membrane, made of cellulose
Freely permeable so substances can pass in and out of the cell
Give the cell shape and keep it rigid, supporting cell
Defense mechanism - protects contents of cell from pathogens

Question 2

What are vacuoles?

Answer 2

Membrane lined sacs in cytoplasm containing cell sap
Many plant cells have large permanent vacuoles which maintain turgor, so the contents of the cell are pushed against the cell wall and maintain a rigid cell framework
Membrane is called tonoplast and is selectively permeable

Question 3

What are chloroplasts?

Answer 3

Responsible for photosynthesis
Often contain DNA and ribosomes, so are able to make own proteins

Double membrane stucture
- fluid enclosed is called stroma
- internal network of membranes form flattened sacs called thykaloids, which when stacked together form granum which are joined by lamellae
- grana contain chlorphyll - light dependent reactions occur during photosythesis
- internal membranes provide large surface area needed for enzymes, proteins and pigment molecules needed for photosynthesis