2.1.2: Organelles

Question 1

What is the structure of the Nucleus?

Answer 1

Nuclear enevelope - double membrane
Nuclear pores
Nucleolus - Smaller sphere inside which is the site of rRNA production and makes ribosomes
Chromosomes - protein head, linear DNA

Question 2

What is the function of the nucleus?

Answer 2

• Site of DNA replication and transcription (making mRNA)
• Contains the genetic code for each cell
• Site of ribosome synthesis

Question 3

What is the structure for the flagella?

Answer 3

Whip like structure

Question 4

What is the function of the flagella?

Answer 4

For mobility, and sometimes as a sensory organelle for chemical stimuli

Question 5

What is the structure of the cilia?

Answer 5

Hairlike projections out of cells

Question 6

What is the function of the cilia?

Answer 6

• Can be mobile or stationary
• Mobile cilia help move substances in a sweeping motion
• Stationary cilia are important in the sensory organs such as the nose

Question 7

What is the structure of the centrioles?

Answer 7

• Made of microtubules
• Occur in pairs to form a centrosome

Question 8

What is the function of centrioles?

Answer 8

Involved in the production of spindle fibre and organisation of chromosomes in cell division

Question 9

What is the structure of the cytoskeleton?

Answer 9

A network of fibres found within the cytoplasm all over a cell
Consists of microfilaments, microtubules and intermediate fibres

Question 10

What is the function of the cytoskeleton?

Answer 10

• Provides mechanical strength to cells, helps maintain shape and stability of a cell. Many organelles are bound to the cytoskeleton
• Microfilaments are respsonsible for cell movement
• Microtubules are responsible for creating a scaffold-like structure

Question 11

What is the structure for the endoplasmic reticulum

Answer 11

• Rough and smooth ER both have folded membranes called cisternae
• RER have ribosomes on the cisternae

Question 12

What is the function of the endoplasmic reticulum?

Answer 12

• RER - protein synthesis (site of)
• SER - it is where lipids and carbohydrates are created and stored

Question 13

What is the structure of the golgi body and vesicles?

Answer 13

• Folded membranes making cisternae
• Secretory vesicles pinch off from the cisternae

Question 14

What is the function of golgi body and vesicles?

Answer 14

• Add carbohydrates to proteins to form glycoproteins
• Produce secretory enzymes
• Secrete carbohydrates
• Transport, modify and store lipids
• Form lysosomes
• Molecules “labelled” with their destination
• Finished products are transported to cell surface in golgi vesicles where they fuse with the membrane and the contents released

Question 15

What is the structure of lysosomes?

Answer 15

Bags of digestive enzymes - can contain 50 different enzymes

Question 16

What is the function of lysosomes?

Answer 16

• Hydrolyse phagocytic cells
• Completely break down dead cells (autolysis)
• Exocytosis - release enzymes outside of the cell to destroy materials
• Digest worn out organelles for reuse of materials

Question 17

What is the structure of the mitochondria?

Answer 17

• Double membrane
• Inner membrane called the cristae
• Fluid centre called the mitochondrial matrix
• Loop of mitochondrial DNA

Question 18

What is the function of the mitochondria?

Answer 18

• Site of aerobic respiration
• Site of ATP production
• DNA to code for enzymes needed in respiration

Question 19

What is the structure of ribosomes?

Answer 19

• Small, made up of two sub-units of protein and rRNA
• 80s - large ribosome found in eukaryotic cells (25nm)
• 70s - smaller ribosome found in prokaryotic cells, mitochondria and chloroplasts

Question 20

What is the function of ribosomes?

Answer 20

Function of protein synthesis

Question 21

What is the structure of chloroplasts?

Answer 21

• Surrounded by a double membrane
• Contains thylakoids (folded membranes embedded with pigment)
• Fluid filled stroma contains enzymes for photosynthesis
• Found in plants

Question 22

What is the function in chloroplasts?

Answer 22

Site of photosynthesis

Question 23

What is the structure of the cell wall?

Answer 23

In plants and fungi cells
* Plants - made of microfibrils of the cellulose polymer
* Fungi - made of chitin, a nitrogen containing polysaccharide

Question 24

What is the function of the cell wall?

Answer 24

Provides structural strength to the cell

Question 25

What is the structure of the plasma membrane

Answer 25

• Found in all cells
• Phospholipid bilayer - molecules embedded within and attached on the outside (proteins, carbohydrates, cholesterol)

Question 26

What is the function of the plasma membrane?

Answer 26

Controls the entrance and exit of molecules

Question 27

What is the process in making and secreting a protein?

Answer 27

1. mRNA copy of the instructions (gene) for insulin is made in the nucleus
2. mRNA leaves the nucleus through the nuclear pore
3. mRNA attaches to a ribosome, in this case attached to a RER. Ribosome reads the instructions to assemble the protein (insulin)
4. Insulin molecules are “pinched off” in vesicles and travel towards golgi body
5. Vesicles fuses with golgi body
6. Golgi body processes and packages insulin molecules ready for release
7. Packaged insulin molecules are “pinched off” in vesicles from golgi body and move towards plasma membrane
8. Vesicle fuses with plasma membrane
9. Plasma membrane opens to release insulin molecules outside