Cell (III) Organelles

Question 1

Explain in Biological terms, what the term “organelle” means?

Answer 1

An organelle is a discrete structure within a cell, having a specific function.

Question 2

Name all the organelles in both animal and plant cell.

Answer 2

Endoplasmic Reticulum (SER/RER)
Golgi Apparatus 
Mitochondria
Microtubules
Cell wall
vacuole
Ribosomes
Lysosomes
Centrioles

Question 3

What are the 2 types of Endoplasmic Reticulum?

Answer 3

Smooth Endoplasmic Reticulum (SER)

Rough Endoplasmic Reticulum (RER)

Question 4

Describe the structure of the Endoplasmic Reticulum.

Answer 4

1) It is a network of folded membranes formed into sheets, tubes/sacs that are extensively interconnected.
2) (RER) has ribosomes attached to the outer surface.
3) SER has no ribosomes, more tubular.

Question 5

What are vesicles?

Answer 5

Vesicles are small, spherical organelle bounded by a single membrane.

Question 6

Mention one fact about the Endoplasmic Reticulum.

Answer 6

The cytoplasm of metabolically active cells is commonly packed with ER.

Question 7

Explain the function of the ER.

Answer 7

1) RER is the site of synthesis of proteins that are ‘packaged in the vesicles. Transport proteins made by the ribosome to Golgi Apparatus for secretion.
2) SER is the site of synthesis of substances needed by a cell. It is important in the manufacture of lipids and steroids, and the reproductive hormones oestrogen and testosterone.

Question 8

Describe the structure of the Golgi Apparatus/ Golgi body/ Golgi complex?

Answer 8

1) It consists of a stack-like collection of flattened membranous sacs.

Question 9

Explain the function of the Golgi Apparatus.

Answer 9

Modify substances made by the endoplasmic reticulum. They store and package these substances in vesicles for secretion out of the cell.

Question 10

Describe the structures of the Mitochondria?

Answer 10

• Metabolically, very active cells will contain thousands of them in their cytoplasm.
  1) Appears mostly as rod-shaped or cylindrical organelles in electron micrographs.
  2) Has a double membrane. Outer membrane is a smooth boundary, inner is infolded to form cristae.
  3) It’s matrix (interior of mitochondrion) contains aqueous solution of metabolites and enzymes, and also small circular lengths of DNA.

Question 11

Explain the functions of the mitochondria?

Answer 11

1) Site where aerobic stages of respiration takes place.
2) Site where synthesis of much ATP. Food is oxidised in aerobic respiration to release energy for cell activities e.g. cell division, growth.

Question 12

Describe the structure of the ribosomes?

Answer 12

Ribosomes are minute structures, approx 25nm in diameter.

It is built of 2 sub-units, and do not have membranes as part of their structures.

It consist of proteins and a nucleic acid known as RNA.

Question 13

Explain the function of ribosomes in a cell.

Answer 13

1) It is the site where proteins are made in a cell. Some of the cell proteins produced have structural roles for instance, collagen.
2) Collagens are biological catalysts -> They cause the reactions of metabolism to occur quickly under the conditions found within the cytoplasm.

Question 14

Describe the structure of lysosomes.

Answer 14

1) They are tiny spherical vesicles bound by a single membrane.
2) They contain a concentrated mixture of ‘digestive’ enzymes. (hydrolytic enzymes), produced in Golgi Apparatus or by RER.

Question 15

Explain the functions of lysosomes.

Answer 15

1) Breakdown of the content of ‘food’ vacuoles.
2) Foreign matter/ food particles taken up into these lysosomes are being broken down. [occurs when lysosome fuse with vacuole]
3) When organelle’s die, the hydrolytic enzymes in lysosomes of cells escape into the cytoplasm and cause self-digestion, known as autolysis.

Question 16

Explain what autolysis is.

Answer 16

The destruction of cells or tissues by their own enzymes, especially those released by lysosomes.

Question 17

Describe the structure of centrioles and microtubules.

Answer 17

Tiny organelle consisting on 9 paired of microtubules arranged in short, hollow cylinder.

Animal cells:

• Centrosome are formed when 2 centrioles occur at right angles, just outside the nucleus.
• Straight, unbranched hollow cylinders, only 25nm wide.
• Made of globular protein called tubulin. This is first built up and then later broken down in the cells as the microtubule frame work is required in different places for different tasks.

Question 18

Function of centrioles and microtubules.

Answer 18

Centrioles:
-Absent in plant cell, they are a small body close to the nucleus that plays a part in cell division.

Microtubules:
-whether plants/ animals, the microtubules are well-organized, which shape and support the cytoplasm.

-Involved in movements of cell components withing the cytoplasm, too, acting to guide and direct organelles.

Question 19

Which organelle helps shape and support the cytoplasm?

Answer 19

microtubules.

Question 20

Which organelle is involved in movement of cell components within cytoplasm?

Answer 20

Microtubules. They are involved in movements of cell components within the cytoplasm, acting to guide and direct organelles.

Question 21

Describe the structure of the chloroplast.

Answer 21

1) Large organelle, biconvex shape.
2) Occur in green plast, where most in the mesophyll cells of leaves.
3) The process that occurs in chloroplast is photosynthesis.
4) Has double membrane:
Outer layer-> continuous boundary.
Inner Layer: In-tucked to form a system of branch8ing membranes called lamellae/ thylakoids.

Question 22

Which organelle is responsible for the process photosynthesis?

Answer 22

Chloroplast. It contains chlorophyll, which traps light energy for photosynthesis.

Question 23

Describe the structure of vacuole in cells.

Answer 23

In animal: small and numerous and temporary.
In plants:
-One large and in the centre of the cell.
- contains cell sap, which is essentially salts and sugar dissolved in water.
-surrounded by a thin membrane called tonoplast, which functions just like the plasma membrane.

Question 24

Explain the function of the vacuole in cells.

Answer 24

1) Store substances in cells such as food and water.

2) Contains cell sap which takes in water and keeps the cell turgid (firm)

Question 25

Is cell wall a organelle? Why or why not.

Answer 25

No, cell wall is not an organelle. As it is a structure external to a cell, but is a product of cell organelles.

Question 26

What does cell wall consist of?

Answer 26

It consist of cellulose, together with other substances, mainly polysaccharides, and are fully permeable.

Question 27

What does it mean to be semi-permeable membrane…

Answer 27

a partially permeable membrane or a differentially permeable membrane, is a membrane that will allow certain molecules or ions to pass through it by diffusion

Question 28

What is the function of the cell wall in plants?

Answer 28

The main functions of the cell wall are to provide structure, support, and protection for the cell.

Question 29

What are plasmodesmata?

Answer 29

Plasmodesmata are cytoplasmic connections between cells, running transversely through the walls, connecting the cytoplasm and adjacent cells.

Question 30

How are plasmodesmata formed?

Answer 30

They are formed when a cell divides and lays down new walls between the separating cell content.

Question 31

Describe the structure of the cilia.

Answer 31

The cilia are organelles that project from the surface of certain cells. They can move and can be up to 10 um long.

They are made up of microtubules coated in plasma membrane.

Question 32

Explain the function of the cilia?

Answer 32

1) They are responsible for movement of organism as a whole.
For instance: Paramecium. cilia cover the surface of the organism and are responsible for movement as well as feeding.

2) They help remove contaminants from organs/ tissues by helping to move fluids over cells. They help remove mucus, bacteria, and other debris from lungs.
3) In Fallopian tubes, the cilia are responsible for helping in fertilization by movement of egg towards the uterus.

Question 33

Describe the structure of the flagella?

Answer 33

1) It occurs singly, typically on small, motile cells, such as sperms, or they may occur in pairs.
2) It is a supramolecular structure composed of about 20 protein components and divided into 3 substructures: the filament, the hook and the basal body.

Question 34

Explain the function of the flagella?

Answer 34

The flagella is a mortality organelle that enables movement of chemotaxis.

Question 35

Name all the organelles in animal cell.

Answer 35

Nucleus, cytoplasm, lysosome, SER, RER, Golgi apparatus, vacuole, mitochondria, centrioles, free ribosomes.

Question 36

Name all the organelles in plant cell.

Answer 36

Cell wall, nucleus, SER, RER, Chloroplast, vacuole, lysosome, mitochondria, cytoplasm, cytoskeleton, Golgi apparatus.

Question 37

What is the difference between animal cell and plant cell?

Answer 37

1) Animal cell have irregular shape while plant cell have regular shape.
2) Vacuole in animal cell is small and numerous whereas vacuole in plant cell is generally a large and one central one.
3) Plant cell has cell wall while animal cell do not.
4) Plant cell have chloroplast while animal cell do not.
5) Plant cells do not have centrosome, but animal cell has centrosome outside the nucleus.
6) The carbohydrate storage product of plant cells are starch but in animal cell, it is glycogen.