IQ1 - Module 1: Cells As A Basis Of Life

Question 1

What is cell theory?

Answer 1

Cell theory states:
1. All living things are made of cells
2. Cells are the basic unit of life
3. All living cells arise from pre-existing cells

Question 2

What is a cell and what can it be classified as?

Answer 2

A cell is the smallest and basic structural and functional unit of an organism.
Cells can be classified as either
- prokaryotic cells
- eukaryotic cells

Question 3

What is a prokaryotic cell?

Answer 3

pro = before karyotic = nucleus
▪ unicellular, e.g. bacteria, archaea
▪ 0.1 to 5.0μm
▪ primitive, less complex
▪ no nucleus
▪ genetic material in a single circular chromosome in the nucleoid with the rest in small circular rings called plasmids
▪ lack membrane bound organelles
▪ large SA:V ratio allowing cells to take in and release materials rapidly and replicate quickly

Question 4

What is a eukaryotic cell?

Answer 4

eu = true karyotic = nucleus
▪ unicellular or multicellular, e.g. plant, animal, fungi, protist (protozoa)
▪ 10 to 100μm
▪ more complex
▪ have a nucleus – where genetic material is found
▪ have membrane bound organelles (each with a specific structure and function)
▪ small SA:V ratio resulting in slower movement of materials

Question 5

What are similar structures between prokaryotic and eukaryotic cells?

Answer 5

These include:
▪ cell membrane ▪ cytoplasm
▪ DNA
▪ ribosomes

Question 6

what can a light microscope see?

Answer 6

The light microscope allowed scientists to observe the first structures in cells including:
▪ Nucleus
▪ Chloroplasts
▪ Cytoplasm
▪ Vacuole
▪ Cell wall
▪ Cell membrane

Question 7

how does a light microscope work

Answer 7

▪ beam of light passes through the specimen and a series of lens to magnify the specimen up to 1500x
▪ one lens is the objective lens and the other lens is the ocular (eyepiece) lens

Question 8

what are staining techniques

Answer 8

The development of specific dyes to stain cells allowed scientists to distinguish different structures of the cell more clearly under the light microscope.

Question 9

what is a fluorescent microscope?

Answer 9

The specimen is labelled with a fluorescent substance, e.g. stains or dyes, that attach to specific structures to be observed.

Question 10

how does a fluorescent microscope work?

Answer 10

▪ similar to a light microscope in that the specimen is illuminated with a high intensity light that causes the fluorescent structures to emit light

Question 11

what is an electron microscope?

Answer 11

The electron microscope allowed scientists to observe the structure of cells in greater detail. All previous structures from the light microscope can be seen providing increased knowledge of their structure and function.
As well as the following structures:
▪ Golgi body
▪ Nucleolus
▪ Mitochondria
▪ Ribosomes
▪ Endoplasmic reticulum
▪ Lysosomes

Question 12

how does a transmitting electron microscope (TEM) work?

Answer 12

▪ beam of electrons are transmitted through the specimen to produce a 2-D image up to 1,500,00x

Question 13

how does scanning electron microscope (SEM) work?

Answer 13

▪ solid specimen is bombarded with a beam of electrons which causes secondary electrons to be emitted from the surface layers of the specimen to produce a 3-D image up to 1,500,00x

Question 14

what is a confocal laser scanning microscope?

Answer 14

Confocal laser scanning microscopes take an image of the specimen allowing a computer program to construct a model.

Question 15

how does confocal laser scanning microscope works?

Answer 15

▪ an image of the specimen is taken at many different levels using laser beams
▪ a computer program is then used to reconstruct a 3-D image / model

Question 16

what does the cell membrane do?

Answer 16

▪ encloses the contents of the cell
▪ controls the movement of substances in and out of the cell
▪ involved in cell recognition and communication with other cells
▪ maintains the internal environment of the cell

This means the cell membrane is a selectively permeable structure that controls the movement of certain molecules and ions between the internal environment (inside the cell) and the external environment (outside the cell).

Question 17

What does selectively permeable mean?

Answer 17

selectively permeable means that the membrane only allows some molecules to pass across and not others. Also referred to as semipermeable.

Question 18

What is the fluid mosaic model?

Answer 18

Our current accepted understanding is based on a model first proposed by Jonathan Singer and Garth Nicholson in 1972.
The fluid mosaic model is widely accepted as the basic model of all biological membranes.

According to this model, the cell membrane structure consists of:
▪ a phospholipid bilayer (two layers)
▪ embedded proteins, carbohydrates and cholesterol

Question 19

what is fluid?

Answer 19

It is not a rigid structure because the phospholipids and some proteins are not in a fixed position. The ability of the phospholipids and proteins to move gives the membrane a fluid nature.
Mosaic
The phospholipid bilayer is embedded with proteins, resulting in a mosaic of many different components

Question 20

what does a phospholipid molecule consist of?

Answer 20

A phospholipid molecule consists of:
Hydrophilic (water-attracting) head composed of a phosphate group
Hydrophobic (water-repelling) tails composed of long-chain fatty acids

Question 21

what is the phospholipid bilayer?

Answer 21

The bilayer has 2 layers of phospholipids arranged with the:
▪ hydrophilic heads in contact with the extracellular fluid outside the cell and intracellular fluid inside the cell
▪ hydrophobic tails meet in the middle

Question 22

what are proteins role in the cell membrane?

Answer 22

Proteins are embedded throughout the membrane. They can be either:
▪ Integral proteins – are permanent and extend through the membrane
▪ Peripheral proteins – are temporary and either bind to integral proteins or partly penetrate one surface of the membrane
Some proteins are fixed in place, but others can travel freely throughout the membrane.

Question 23

what are the different kinds of proteins with a specific function called?

Answer 23

There are different kinds of proteins each with a specific function, such as :
▪ transport channels
▪ receptor binding sites for various substances, e.g. hormones, that trigger a response in the cell

Question 24

what are carbohydrates in the cell membrane and its role?

Answer 24

Carbohydrates are attached to some surface proteins forming glycoproteins and to lipids forming glycolipids.

They have an important role in cell-cell interactions, such as:
▪ the recognition and adhesion between cells
▪ acting as a marker molecule on the surface of cells (this is important in the body’s defence by recognising ‘self’ (own) cells compared to ‘non-self’ (foreign, e.g. bacteria) cells)

Question 25

what is cholesterol in the cell membrane?

Answer 25

Cholesterol molecules are embedded within the membrane between phospholipid molecules providing stability to the cell membrane without affecting its fluidity.

Cholesterol molecules are embedded within the membrane between phospholipid molecules providing stability to the cell membrane without affecting its fluidity.