S1) Basic Cell Structure

Question 1

State the structure and function of the following:

• Nucleus
• Nucleolus
• Nuclear membrane

Answer 1

• Nucleus – cell’s control centre, contains chromatin and DNA
• Nucleolus – the region at the centre of the nucleus; role in ribosome production (stains dark)
• Nuclear membrane – a two-layered selectively-permeable membrane with pores for passage of substances

Question 2

State the structure and function of the following:

• Microtubules
• Centriole
• Microvillii

Answer 2

• Microtubules – part of the cell’s cytoskeleton, aid movement of substances through cytoplasm
• Centriole – composed of two cylinders of tubules; essential to cell reproduction
• Microvilli – projections which increase the cell’s surface area

Question 3

State the structure and function of the following:

• Microfilament
• Vacuole
• Cytoskeleton

Answer 3

• Microfilament – provides support for the cell; sometimes linked to cell’s outer membrane
• Vacuole – sac that stores and transport ingested materials, waste products and water
• Cytoskeleton – internal framework of the cell, made up of microfilaments and hollow microtubules

Question 4

State the structure and function of the following:

• Cytoplasm
• Ribosome
• Cell membrane

Answer 4

• Cytoplasm –fluid in which organelles float; primarily water, contains enzymes and amino acids
• Ribosome – tiny structure that assists with protein assembly
• Cell membrane – encloses contents of the cell and maintains the cell’s shape; regulates passage of substances

Question 5

State the structure and function of the following:

• Lysosome
• sER
• rER

Answer 5

• Lysosome – produces hydrolytic enzymes that aid in digestion and excretion of substances
• sER – network of tubes and flat curved sacs that helps to transport materials through the cell; main location of fat metabolism
• rER – folded membranes studded with ribosomes, helps transport of materials through the cell; site of protein manufacture

Question 6

State the structure and function of the following:

• Golgi complex
• Mitochondrion

Answer 6

• Golgi complex – a structure that processes and repackages proteins produced in the rER for release at the cell membrane
• Mitochondrion – site of fat and sugar digestion in the cell (cellular respiration), produces energy

Question 7

What are the two types of chromatin?

Answer 7

• Chromatin is found in two varieties: euchromatin and heterochromatin
• Heterochromatin stains more intensely, indicating tighter packing

Question 8

What is limit of resolution?

Answer 8

Limit of resolution – the minimum distance at which two objects can be distinguished

Question 9

Outline the general structure of prokaryotic cells

Answer 9

• Prokaryotic cells have an external membrane but no internal membranes
• All the biochemical processes of the cell occur in the same compartment

Question 10

Identify 7 primary components of the prokaryotic cell

Answer 10

• Capsule
• Cell wall
• Plasma membrane
• Flagella
• 70s Ribosomes
• Nucleoid
• Pili

Question 11

Outline the general structure of a eukaryotic cell

Answer 11

• Eukaryotic cells are compartmentalised by internal membranes
• Hence, eukaryotic cells have a true nucleus and true organelles

Question 12

Identify 10 primary components of the eukaryotic cell

Answer 12

• Plasma membrane
• Vacuole
• Nuclear envelope
• Nucleolus
• Chromosomes
• Lysosome
• rER and sER
• Golgi Complex
• Free ribosomes
• Mitochondria

Question 13

Describe the structure of plasma membranes

Answer 13

• Composed of a phospholipid bilayer
• Ampipathic
• Associated membrane proteins: Integral and peripheral proteins

Question 14

Describe 5 functions of the plasma membrane

Answer 14

• Selective permeability
• Transport of materials along cell surface
• Endocytosis and exocytosis
• Intercellular recognition
• Barrier to water-soluble molecules

Question 15

What is glycocalyx?

Answer 15

• The glycocalyx is the cell coat
• It is made up of oligosaccharide and polysaccharide side chains on the outside of the plasma membrane

Question 16

Outline 4 features of the Fluid Mosaic Model

Answer 16

• Hydrophobic fatty acid tails in the middle
• Hydrophilic heads on the outside
• Membrane proteins: integral proteins, peripheral proteins
• Phospholipids form a bi-layer

Question 17

Describe the structure of the endoplasmic reticulum

Answer 17

• ER membrane is continuous and encloses a single lumen
• sER does not have ribosomes attached
• rER has ribosomes attached

Question 18

Distinguish between free and bound polyribosomes in terms of protein production

Answer 18

• Free polyribosomes synthesise proteins which remain in the cytoplasm
• Bound polyribosomes show protein synthesis and segregation into the rough ER

Question 19

Describe the role of the Golgi apparatus in the cell

Answer 19

The Golgi apparatus functions to modify, sort, concentrate and package proteins synthesised on the rough endoplasmic reticulum

Question 20

Outline the structure and function of lysosomes

Answer 20

- Structure: generated by the Golgi apparatus and contain many hydrolytic enzymes

• Function: fuse with material requiring digestion

Question 21

Distinguish between primary and secondary lysosomes in terms of their formation and function

Answer 21

• Primary lysosome:

I. Formed from the Golgi apparatus

II. Does not release intracellular contents

• Secondary lysosome:

I. Formed by the fusion of the primary lysosome and an endocytotic/phagocytotic vesicle

II. Releases intracellular contents/waste products

Question 22

Describe the structure and function of mitochondria

Answer 22

• Structure: double membrane, DNA, ribosomes and division similar to bacteria
• Function: ATP generation by oxidative phosphorylation

Question 23

How are mitochondrias inherited?

Answer 23

Female lineage

Question 24

Identify 4 functions of the cytoskeleton

Answer 24

• Determines the shape of animal cells
• Ensures movement of cells
• Structural support and movement of cell organelles
• Provides the framework for moving and separating cells during cell division

Question 25

What are microtubules?

Answer 25

**Microtubules** are long hollow cylinders made of the protein tubulin

Question 26

Where are microtubules found?

Answer 26

Sites where structures are moved (i.e. nerve fibres, the mitotic spindle, cilia and flagella)