Levels of Organisation

Question 1

What is a cell?

Answer 1

The smallest structural & functional unit of the living organism.

Question 2

What is a tissue?

Answer 2

A group of modified cells specialized to perform specific function
E.g.: Epithelial, connective, muscle and nervous

Question 3

What is an organ?

Answer 3

A group of tissues which perform a specific function

Question 4

What is an organ system?

Answer 4

A group of organs which perform a related function

Question 5

List the organelles of the cell?

Answer 5

Cell membrane, cytoskeleton, microtubules, cytoplasm, nucleus, rough ER, smooth ER, Golgi apparatus, mitochondria, secretory vesicles, lysosomes, peroxisomes and endosomes

Question 6

Mitochondria

Answer 6

Oval shaped structure
Double layer structure - inner membrane folded into cristae
Granular matrix inside the mitochondria

Functions include generation of ATP, cell cycle, cell growth control and apoptosis

Question 7

Ribosomes

Answer 7

Made from 2 subunits
Subunits made from proteins

Can either be free in the cytoplasm or attached to rER

Translate mRNA into protein

Polyribosomes: Ribosomes found in clusters held together by RNA strand

Question 8

Rough ER

Answer 8

Formed from interconnected network of tubules and vesicles
Studded with ribosomes
Involved in synthesis and packaging of proteins

Question 9

Smooth ER

Answer 9

Synthesize fatty acids and steroids
Detoxify drugs in liver
Breakdown glycogen and form glucose
Ca++ store and release
Segregates newly synthesized proteins from cytoplasm

Question 10

Golgi Apparatus

Answer 10

Flattened membranous sacs
Closely associated with rER
Have concave side (cis face) located near ER - receiving end of proteins
Convex side (trans face) - “shipping” end proteins

Involved in processing proteins
Storage and transport of material out of the cell

Question 11

Lysosomes

Answer 11

Vesicles produced by Golgi Apparatus
Contain acid hydrolases (hydrolysing enzymes)

Breakdown waste material and cellular debris

Question 12

Phagosomes

Answer 12

Vacuoles formed by fusion of cell membrane around the particle

Question 13

Peroxisomes

Answer 13

Membrane bound organelles
Present in all cells; prominent in hepatocytes and in proximal tubule cells
Contain oxidative enzymes for:
1. Hydrogen peroxide metabolism
2. Fatty acid metabolism
3. Alcohol degradation
4. Formation of specialised phospholipid that is needed for myelination of nerve cells.

Question 14

Nucleus

Answer 14

Contains chromatin and the nucleolus
Structure is surrounded by nuclear envelope

Storage and transmission of genetic material

Question 15

Nuclear envelope

Answer 15

Double layered structure forming selective barrier between nucleus and cytoplasm
Outer membrane consistent with rough ER
Inner membrane lined with nuclear lamina (condensation of intermediate filaments) - maintains nucleus shape
Outer and inner membranes of the nuclear envelope fuse to form numerous nuclear pores
Pores control the movement of ribosomal subunits between the nucleus and cytoplasm.

Question 16

Chromatin

Answer 16

Chromatin/DNA encodes the cell structure and functions

Question 17

What are the 2 states of chromatin?

Answer 17

1. Heterochromatin: Inactive; stains dark

2. Euchromatin: Active; light staining

Question 18

Nucleolus

Answer 18

Dark-staining spherical body
Not bound by a membrane
Contains RNA and protein
Site of ribosome synthesis

Question 19

Cytoskeleton

Answer 19

Maintain cellular architecture, facilitate motility and divide the cytosol into functional discrete areas

Question 20

What are the classifications of cytoskeletons?

Answer 20

According to the thickness they are divided into:

1. Microtubules (composed of tubulin subunits) 25 nm thick
2. Intermediate filaments 10 nm thick
3. Microfilaments (mostly actin) 7 nm thick

Question 21

Microtubules

Answer 21

Hollow tubes present in all cell types except red blood cells
Made of spherical protein tubulin
Responsible for intracellular movement of cytoplasmic organelles
Form centrioles
Form cilia and flagella

Question 22

Intermediate filaments

Answer 22

Tough, insoluble protein fibers with high tensile strength

Resist pulling forces on the cell

Question 23

Microfilaments

Answer 23

The strands of the protein actin
Attached to the cytoplasmic side of the plasma membrane
Braces and strengthens the cell surface

Question 24

Centrosomes and centrioles

Answer 24

Centrosomes are an area of the cytoplasm located near the nucleus
Within centrosome: 2 small cylindrical structures called centrioles
Centrioles = small barrel-shaped organelles formed of pinwheel array of 9 triplets of microtubules

During cell division centrioles move to the opposite poles of the cell, where organize spindles that control the distribution of chromosomes to the daughter cells.

Question 25

What are the forms of cellular extensions?

Answer 25

1. Cilia
2. Flagella
3. Microvilli
4. Sterocilia

Question 26

Cilia

Answer 26

Short cell projection composed of nine pairs of microtubules surrounding a central pair
They move fluid in a single direction across the cell surface.

Question 27

Flagella

Answer 27

Longer than cilia, e.g., tail of the human sperm.

Question 28

Microvilli

Answer 28

Tubular extensions of plasma membrane which contain bundle of actin filaments

Increase surface area for absorption

Question 29

Sterocilia

Answer 29

Modified microvilli seen on cells in the epididymis.
Length and bundle arrangement differentiate them from microvilli

Increase surface area for absorption