Topic 3 - Cell Structure

Question 1

What is the structure of the nuclear envelope?

Answer 1

It’s a double membrane surrounding the nucleus. It’s outer membrane is continuous with the endoplasmic reticulum of the cell and often has ribosomes on the surface.

Question 2

What is the function of the nuclear envelope?

Answer 2

It’s function is to control the entry and exit of materials in and out of the nucleus and controls the reactions taking place within it

Question 3

What’s the function of nuclear pores?

Answer 3

They allow the passage of large molecules such as mRNA out of the nucleus

Question 4

What is the nucleoplasm?

Answer 4

It’s a granular, jelly-like material that makes up the bulk of the nucleus

Question 5

What’s the nucleolus?

Answer 5

A small spherical region within the nucleoplasm. It manufactures ribosomal RNA and assembles the ribosomes.

Question 6

What are the functions of the nucleus?

Answer 6

• Act as the control centre of the cell through the production of mRNA and tRNA and hence protein synthesis
• Retain the genetic material of the cell in the form of DNA and chromosomes
• Manufacture ribosomal RNA and ribosomes

Question 7

What are the main structures of the mitochondria?

Answer 7

Double membrane : cristae and matrix

Question 8

Describe cristae.

Answer 8

They’re extensions of the inner membrane, which in some species extend across the whole width of the mitochondrion. These provide a large surface area for the attachment of enzymes and other proteins involved in respiration

Question 9

Describe the matrix.

Answer 9

Makes up the remainder of the mitochondrion (not cristae). It contains proteins, lipids, ribosomes and DNA that allows the mitochondria to control the production of some of their own proteins. Many enzymes involved in respiration are found in the matrix.

Question 10

What’s the chloroplast envelope?

Answer 10

A double plasma membrane that surrounds the organelle. It is highly selective in what it allows to enter and leave the chloroplast.

Question 11

What are the grana?

Answer 11

Stacks of 100 disc-like structures called thylakoids.

Question 12

What are chlorophyll?

Answer 12

Photosynthetic pigments within in thylakoids

Question 13

What’s the stroma?

Answer 13

A fluid filled matrix where the second stage of photosynthesis takes place. Wishing the storm are a number of other structures such as starch grains

Question 14

How are chloroplasts adapted to photosynthesis?

Answer 14

⭐︎The granal membranes provide a large SA for the attachment of chlorophyll, electron carriers and enzymes that carry out the first stage of photosynthesis
⭐︎The fluid of the stroma possesses all the enzymes needed to make sugars in the second stage of photosynthesis
⭐︎Chloroplasts contain both DNA and ribosomes so can quickly and easily manufacture some of the proteins needed for photosynthesis

Question 15

Functions of the rough endoplasmic reticulum

Answer 15

• Provide a large surface area for the synthesis of proteins and glycoproteins
• Provide a pathway for the transport of materials, especially proteins, throughout the cell

Question 16

Functions of the smooth endoplasmic reticulum

Answer 16

• Synthesise, store and transport lipids

- Synthesise, store and transport carbohydrates

Question 17

Functions of the Golgi apparatus.

Answer 17

○Add carbohydrates to proteins to form glycoproteins
○Produce secretory enzymes
○Secrete carbohydrates e.g. those used in making cell walls in plants
○Transport, modify and store lipids
○Form lysosomes

Question 18

Functions of lysosomes.

Answer 18

⭐︎Hydrolyse material ingested by phagocytic cells
⭐︎Release enzymes to the outside of the cell (exocytosis) in order to destroy material around the cell
⭐︎Digest worn out organelles so that the useful chemicals they are made of and can be re-used
⭐︎Completely breakdown cells after they have died (autolysis)

Question 19

Structure of ribosomes.

Answer 19

Small cytoplasmic granules with two sub-units - one small and one large each containing ribosomal RNA and protein.

Question 20

Two types of ribosome and where they’re found

Answer 20

80S - found in eukaryotic cells, around 25nm in diameter

70S - found in prokaryotic cells, mitochondria and chloroplasts - is slightly smaller

Question 21

Features of the cell wall?

Answer 21

• They consist of a number of polysaccharides such as cellulose
• There is a thin layer, called the middle lamella, which marks the boundary between adjacent cell walls and cements adjacent cells together

Question 22

Functions of the cellulose cell wall

Answer 22

• Provide mechanical strength in order to prevent the cell bursting under the pressure created by the osmotic entry of water
• To give mechanical strength to the plant as a whole
• To allow water to pass along it and so contribute to the movement of water through the plant