Eukaryotic cell stucture

Question 1

What is the importance of the nucleus?

Answer 1

Contains the organism genetic material and controls the cell’s activities.

Question 2

What is the nuclear envelope ands its function?

Answer 2

A double membrane that surrounds the nucleus, Its outer membrane is continuous with the endoplasmic reticulum of the cell and often has ribosomes on its surface.

It controls materials entering and exiting the nucleus.

Question 3

What are the nuclear pores?

Answer 3

Allow molecules synthesised in the nuclear to leave the cytoplasm.

Question 4

What is the nucleolus?

Answer 4

The site of ribosome synthesis.

Question 5

What is the cell surface membrane?

Answer 5

Mainly made of lipids and proteins, and controls what enters and leaves the cell.

Question 6

What is the structure of the mitochondria?

Answer 6

A double membrane that controls the entry and exit of material.
The inner membrane is folded to form extensions- ‘cristae’- provide a large surface area for the attachment of enzymes and other proteins for respiration.
The ‘matrix’ makes up the remainder of the mitochondrion,contains metabolites, enzymes and DNA that allow the mitochondria to control the production of their own proteins.

Question 7

What is chromatin?

Answer 7

Contains instructions to make proteins.

Question 8

What is function of mitochondria?

Answer 8

Site of respiration, so produces ATP (universal energy-carrier; drives almost all chemical reactions).

Question 9

What is the chloroplast envelope?

Answer 9

A double membrane surrounding the organelle, is highly selective in what it allows to enter and leave the chloroplast.

Question 10

What is the grana?

Answer 10

The inner membrane becomes folded forming thylakoids, are arranged in flattened circular piles- grana.
Some thylakoids have tubular extensions that join up with thylakoids in adjacent grana.

Question 11

Where is the chlorophyll contained?

Answer 11

In the thylakoids.

Question 12

What is the stroma?

Answer 12

A fluid-filled matrix, containing enzymes, starch grains and DNA.

Where the second stage of photosynthesis takes place- synthesis of sugars.

Question 13

How are the chloroplasts adapted to their function of harvesting sunlight and carrying out photosynthesis?

Answer 13

• the granal membranes provide a large surface area for the attachment (in a highly order fashion) of chlorophyll, electron carriers and enzymes for light absorption.

• The fluid of the stroma contains all the enzymes needed to make sugars in the second stage of photosynthesis.

• chloroplasts contain both DNA and ribosomes to easily and quickly manufacture some of the proteins needed for photosynthesis.

Question 14

What is the endoplasmic reticulum?

Answer 14

Three- dimensional system of sheet-like membranes, spreading through the cytoplasm of the cell.
Is continuous with the nuclear envelope.
The membranes enclose a network of tubules and flattened sacs- cisternae.

Cells that manufacture and store large quantities of carbs, lipids and proteins have a very extensive ER, e.g liver cells.

Question 15

What is the rough endoplasmic reticulum?

Answer 15

Single membrane bound in sacs studded with ribosomes.
Functions:
- provides a large surface area for the synthesis of proteins and glycoproteins.
- provides a pathway for the transport of materials (especially proteins) throughout the cell.

Question 16

What is the smooth endoplasmic reticulum?

Answer 16

Single membrane, lacks ribosomes but often more tubular in appearance.
Function:
- synthesise, store and transport lipids, phospholipids, steroids and carbohydrates.
- store calcium ions (important for muscle contraction)

Question 17

What is the structure of the Golgi apparatus?

Answer 17

Single membrane, consists of stacks of membranes that make up flattened sacs called cisternae, with vesicles- small rounded hollow structure.

Question 18

What is the function of the Golgi apparatus?

Answer 18

• transport, modify and store lipids and proteins ready for secretion .
• form lysosomes.
• add carbohydrates to proteins to form glycoproteins.
• produce secretory enzymes, such as those secreted by the pancreas.
• Secrete carbohydrates such as those used in making cell walls in plants.

Question 19

What is the role of the the Golgi body?

Answer 19

The proteins and lipids produced by the ER are passed through the Golgi apparatus in a strict sequence. The Golgi modifies these proteins often by adding non- protein components, such as carbohydrate, to them.
It also ‘labels’ them, allowing them to be accurately sorted and sent to their correct destination. Once sorted, the modified proteins and lipids are transported in Golgi vesicles which are regularly pinched off from the end of the Golgi cinsternae. These vesicles may move to the cell surface, where they fuse with the membrane and release their contents outside.

Question 20

What are Golgi vesicles?

Answer 20

Small fluid filled sacs in the cytoplasm, surrounded by a single membrane and produced by the Golgi apparatus.

Question 21

What are lysosomes?

Answer 21

Small spherical vesicle produced by the Golgi apparatus, that contain enzymes such as protease and lipase. They also contain lysozymes enzymes that hydrolyse the cell walls of certain bacteria.

Question 22

What is the function of lysosomes?

Answer 22

• hydrolyse material ingested by phagocytic cells eg white blood cells and bacteria.
• release enzymes to the outside of the cell in order to destroy material around the cell.
• digest worn out organelles so that the useful chemicals they are made of can be reused.
• completely break down cells after they have died (autolysis).

Question 23

What are ribosomes?

Answer 23

Small cytoplasmic granules found in the cytoplasm or studded on the RER of all cells.

Question 24

What are the types of ribosomes?

Answer 24

80S- found in eukaryotic cells, around 25nm in diameter.
70S- found in prokaryotic cells, mitochondria, and chloroplasts, slightly smaller.

Question 25

What is the structure of the ribosomes?

Answer 25

2 sub-units: one large and one small, both containing ribosomal RNA and protein.
Have no membrane.

Question 26

What is the function of ribosomes?

Answer 26

Site of protein synthesis

Question 27

What is the structure of cell walls in plants and algae?

Answer 27

Consists of microfibrils of polysaccharide cellulose, embedded in a matrix, which have considerable strength so contribute to the overall strength of the cell wall.

Includes middle lamella- thin layer marking the boundary between adjacent cell walls and cements adjacent cell walls together.

Question 28

What are functions of the cellulose cell wall?

Answer 28

• to 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’s shape.
•contribute to the movement of water through the plant.

Question 29

What is the cell walls of fungi made of?

Answer 29

chitin, glycan and glycoproteins

Question 30

What is the structure of vacuoles?

Answer 30

A fluid filled sac founded by a single membrane (tonoplast).
A plant vacuole contains a solution of mineral salts, sugars, amino acids, wastes and sometimes pigments such as anthocyanins.

Question 31

What are the functions of plant vacuoles?

Answer 31

• support herbaceous plants by making cells turgid.
• the sugars and amino acids may act as a temporary food source.
• the pigments may contain petals to attract pollinating insects.