Chapter 2 - Cells and Organelles

Question 1

What are the 2 types of cells?

Answer 1

Eukaryotic and Prokaryotic

Question 2

Nucleus

Answer 2

• contains coded genetic info in the form of DNA molecules
• DNA controls the metabolic activities of the cell
• DNA is contained within a nuclear envelope (double membrane)
• Nuclear envelope has nuclear pores - allow molecules to move in and out the nucleus
• DNA+histones=chromatin-> coil and condense to form chromosomes

Question 3

Nucleolus

Answer 3

• within the nucleus + responsible for ribosome production
• composed of RNA +proteins
• RNA = produce rRNA, then combine with proteins=ribosomes for protein synthesis

Question 4

Mitochondria

Answer 4

-site of aerobic respiration, where ATP is produced
- number of mitochondria in a cell reflects how much energy used
-double membrane
the inner membrane is folded to form cristae and fluid interior=matrix
-inner membrane contains enzymes used in aerobic respiration
-can produce their own enzymes and reproduce themselves

Question 5

Vesicles

Answer 5

• membranous sacs that have storage and transport roles
• only have a single membrane with fluid inside
• transport materials inside the cell

Question 6

Lysosomes

Answer 6

• specialised vesicles that contain hydrolytic enzymes
• break down waste material in cells
• break down pathogens ingested by phagocytic cells
• programmed cell death- apoptosis

Question 7

Cytoskeleton

Answer 7

• network of fibres necessary for shape and stability of cell

Question 8

What are the 4 main functions of the cytoskeleton?

Answer 8

• Microtubules and microfilaments support the cell’s organelles, keeping them in position
• strengthen the cell and main shape
• responsible for movement of materials within the cell
• proteins of cytoskeleton can also cause the cell to move

Question 9

Microfilaments

Answer 9

-responsible for cell movement and cell contraction during cytokinesis

Question 10

Microtubules

Answer 10

• globular proteins polymerise to form tubes
• tracks for the movement of organelles around the cell
• spindle fibres are composed of microtubules

Question 11

Intermediate fibres

Answer 11

-mechanical strength in cells and help maintain their integrity

Question 12

Centrioles

Answer 12

• small hollow cylinders composed of microtubules

- 2 associated centrioles form the centrosome

Question 13

Cilia

Answer 13

• small, hair-like structures on surface membrane of some animal cells
• cross section -> outer membrane and ring of 9 pairs of protein microtubules inside, with 2 microtubules in the middle
• microtubules allow cilia to move - used by the cell to move substances along the cell surface

Question 14

Flagella

Answer 14

• enable cells motility
• stick out from cell surface and surrounded by plasma membrane
• inside is the same as cilia - 9 pair of microtubules around the edge, 2 in the centre
• microtubules contract to make it move

Question 15

Smooth endoplasmic reticulum

Answer 15

-network of membranes enclosing flattened sacs (cisternae)
-responsible for lipid and carbohydrate synthesis, and storage
(synthesis and processes lipids)

Question 16

Rough endoplasmic reticulum

Answer 16

• network of membranes enclosing flattened sacs (cisternae)
• ribosomes on its surface
• responsible for synthesis + transport of proteins
• FOLD AND PROCESS PROTEINS

Question 17

Ribosomes

Answer 17

• free-floating in the cytoplasm/ attached to the ER, forming RER
• constructed of RNA molecules made in the nucleolus of the cell
• site of protein synthesis

Question 18

Golgi apparatus

Answer 18

• compact structure formed of cisternae+no ribosomes
• modify proteins and package them into vesicles
• secretory vesicles/lysosomes

Question 19

Protein production

Answer 19

• Proteins are synthesised on the ribosomes bound to the ER
• pass on its cisternae and are packaged into transport vesicles
• vesicles containing the newly synthesised proteins move towards the Golgi via the cytoskeleton transport
• Vesicle fuse with the golgi and protein enter
• protein is modified and leaves the golgi in vesicles
• secretory vesicles carry proteins that are to be released from the cell
• vesicles move towards and fuse with the cell-surface membrane, released by exocytosis

Question 20

Cell wall

Answer 20

• made of cellulose
• freely permeable-> substances pass in and out of the cell through the cellulose wall
• make it rigid
• supports the plant
• defence mechanism- against invading pathogens

Question 21

Vacuoles

Answer 21

• membrane lined sacs in the cytoplasm containing cell sap
• many plant cells have permanent vacuoles-> maintenance of turgor
• membrane of vacuole=tonoplast
• selectively permeable-some small molecules can pass through it

Question 22

Chloroplasts

Answer 22

• responsible for photosynthesis in plant cells
• found in the cells in the green parts of plants like leaves and stems
• double membrane structure
• fluid enclosed in the chloroplast= stroma
• internal network of membranes=thylakoids
• thylakoids stacked together=granum
• grana are joined by a lamellae
• grana contains the chlorophyll
• also contains its own DNA and ribosomes

Question 23

Features of prokaryotes

Answer 23

PROKARYOTES: (bacterial cells)

• extremely small cells (<2 um diameter)
• DNA is circular
• No nucleus - DNA free in cytoplasm
• Cell wall made of polysaccharide but not cellulose/chitin
• Few organelles and no membrane-bound organelles eg mitochondria
• Flagella made of the protein flagellin, arranged in a helix
• small ribosomes

Question 24

Eukaryotes features

Answer 24

• larger cells (approx 10-100 um diameter)
• DNA is linear
• Nucleus is present-> DNA is inside the nucleus
• No cell wall
• Many organelles are membrane bound
• flagella made of microtubule proteins

-larger ribosomes