Plant Cells

Question 1

What are the two forms of starch?

Answer 1

Amylose and amylopectin

Question 2

Describe the structure of cellulose

Answer 2

• made up of a very long beta-glucose chain
• joined by 1-4 glycosidic bonds, in condensation reactions
• alternate B-glucoses are rotated 180•
• hydroxyl (OH) groups project from both sides of the chain

Question 3

How is cell wall structure related to its function?

Answer 3

Provides strength and support for plants; strength comes from micro fibrils (bundles of 60/70 straight unbranched cellulose molecules lying parallel, held together by strong hydrogen bonds between OH groups)

Question 4

How are microfibrils stuck together?

Answer 4

Polysaccharide ‘glue’ made from short branches polysaccharides, hemicelluloses (polymers of sugar other than glucose) and pectins (polymers of a sugar acid)

Question 5

What is the middle lamella?

Answer 5

Outermost layer of plant cells and acts like glue to stick adjacent plant cells together —> provides stability to cell

Question 6

What is the plasmodesmata?

Answer 6

Narrow threads of cytoplasm surrounded by a cell membrane which connect the cytoplasm of neighbouring plant cells —> allows substances to be transported between plant cells and facilitates cell-cell communication

Question 7

What are pits?

Answer 7

-Very thin regions of the cell wall, lined up in pairs, which facilitates transport of substances between cells

Question 8

What are chloroplasts and their structure?

Answer 8

Larger than mitochondria, surrounded by double membrane
-membrane-bound compartments called thylakoids containing chlorophyll stack to fork structures called grana.
- grana are joined together by lamellae ( thin and flat thylakoid membranes)
- site of photosynthesis
- also contain small circular DNA and ribosomes used to synthesise proteins needed in chloroplast replication and photosynthesis

Question 9

What are amyloplasts?

Answer 9

Small membrane bound organelles containing starch granules; store starch in plants and convert it back to glucose when the plant needs

Question 10

What are vacuoles?

Answer 10

A sac in plant cells surrounded by the tonoplast (selectively permeable membrane), contains cell sap made up of water, minerals, waste + enzymes
- keeps cells turgid, can break down + isolate unwanted chemicals, tonoplasts control entry + exit of substances

Question 11

Describe structure and function of glycogen

Answer 11

~ Storage form of energy in animals
~ made up of alpha glucose, 1,4 and 1,6 glycosidic bonds, branched to allow more ends to hydrolyse