Cells

Question 1

Cell

Answer 1

The basic structural and functional unit of all organisms; the smallest structure capable of performing all the activities vital to life.

The cell is the basic, living, structural and functional unit of the body.

IMAGE 3.1 in Wiley

Question 2

Cell division

Answer 2

Process by which a cell reproduces itself that consists of a nuclear division (mitosis) and a cytoplasmic division (cytokinesis); types include somatic and reproductive

Question 3

Cell biology

Answer 3

The study of cellular structure and function

A.K.A. Cytology

Question 4

What are the three main parts of a cell

Answer 4

The plasma membrane,
The cytoplasm,
The nucleus

Question 5

The plasma membrane

Answer 5

Forms a cell’s flexible outer surface.
This separates the inside of the cell from the outside of the cell.
It also regulates the flow of materials in and out of the cell, maintaining the appropriate environment for normal cellular activities.
It also plays a key role in communication among cells and between cells and their external environment.

Question 6

The cytoplasm

Answer 6

Is formed of all the cellular contents between the plasma membrane and the nucleus.
It has two components; cytosol and organelles.
Cytosol is the liquid portion that mostly consists of water plus dissolved solutes and suspended particles. Cytosol a.k.a intracellular fluid.
There are different types of organelles in the cytosol,each with a characteristic structure and specific functions.

Question 7

The nucleus

Answer 7

Is the largest organelle.
It acts as a control centre for a cell because it contains the genes, which control cellular structure and most cellular activities.

Question 8

The structure of the plasma membrane

Answer 8

A flexible yet sturdy barrier.
Mostly made up of lipids and proteins.
Lipid bilayer is the basic framework - two tail to tail layers made of three types of lipid molecules.
Phospholipids(lipids containing phosphorous), cholesterol and glycolipids (lipids attached to carbohydrates).
The proteins in a membrane are of two types - integral and peripheral.
Integral proteins extend into or through the lipid bilayer.
Peripheral proteins are loosely attached to the interior to exterior surface of the membrane.
Some peripheral proteins called glycoproteins are attached to carbohydrates.
The plasma membrane consists of mostly phospholipids, arranged in a bilayer, and proteins, most of which are glycoproteins.

Question 9

The functions of the plasma membrane

Answer 9

Acts as a barrier separating inside and outside of the cell
Controls the flow of substances into and out of the cell
Helps identify the cell to other cells -e.g. Immune cells
Participates in intercellular signalling

Question 10

Functions of membrane proteins

Answer 10

Some integral proteins function as channels or carriers to move substances across membranes.
Other integral proteins function as receptors.
Membrane glycolipids and glycoproteins are involved in cellular recognition.

Question 11

What is selective permeability of the plasma membrane?

Answer 11

Selective permeability allows some substances to move into and out of the cell but restricts the passage of other substances.
The lipid bilayer is permeable to water and nonpolar (lipid-soluble) molecules e.g. Fatty acids, fat-soluble vitamins, steroids, oxygen and carbon dioxide.
The lipid bilayer is not permeable to ions and large, uncharged polar molecules e.g. Glucose and amino acids.
These small and medium sized water-soluble materials may cross the membrane with the assistance of integral proteins.
Large molecules are unable to pass through the plasma membrane except by transport within vesicles.

Question 12

How do integral proteins assist small and medium sized water-soluble materials across the plasma membrane?

Answer 12

Some integral proteins form ion channels through which specific ions e.g. Potassium ions can move into and out of cells. Other membrane proteins act as carriers (transporters), which change shape as they move a substance from one side of the membrane to the other.

Question 13

What do most functions of the plasma membrane depend on?

Answer 13

Most functions of the plasma membrane depend on the types of proteins that are present.
Integral proteins called receptors recognise and bind a specific molecule that governs some cellular function e.g. A hormone such as insulin.
Some integral proteins act as enzymes, speeding up specific chemical reactions.
Membrane glycoproteins and glycolipids often are cell identity markers. They enable a cell to recognise other cells of its own kind during tissue formation, or to recognise and respond to potentially dangerous foreign cells

Question 14

What is intracellular fluid?

Answer 14

The fluid contained within cells. The cytosol of a cell.

About two thirds of fluid in body is intracellular fluid (ICF)

Question 15

What do you call the fluid outside of cells?

Give 2 examples (there are 4)

Answer 15

Extracellular fluid (ECF).
E.g. Interstitial fluid (a.k.a inter cellular or tissue fluid) fluid that is in the microscopic spaces between cells of tissues.
Blood plasma the ECF in blood vessels.
ECF in lymphatic vessels is called lymph
ECF within and around the brain and spinal fluid is called cerebrospinal fluid (CSF)

Question 16

What materials can be dissolved in body fluids?

Answer 16

Gases, nutrients, ions and other substances needed to maintain life.

Question 17

Describe body fluids then explain concentration gradients

Answer 17

Body fluids are dilute solutions in which a variety of solutes (any material dissolved in a fluid) are dissolved in a familiar solvent (the fluid in which solutes are dissolved), water.
The amount of solute in a solution is its concentration.
A concentration gradient is a difference in concentration between two different area e.g. ICF and ECF.
Solutes moving from a high concentration to a low concentration area are said to move down or with the concentration gradient.
Solutes that are moving from a low concentration area to a high concentration area are said to move up or against the concentration gradient.

Question 18

What do you call it when a substance moves down its concentration gradient through the membrane, using only its own kinetic energy (energy of motion) including simple diffusion and osmosis?

Answer 18

Passive processes

Question 19

What happens in active processes?

Answer 19

Cellular energy, usually ATP, “pushes” the substance through the membrane “uphill” against its concentration gradient.
E.g. Active transport
Another active process allows substances to enter and leave cells by using tiny membrane sacs (vesicles).

Question 20

Net diffusion

Answer 20

The diffusion of more molecules in one direction than the other, down their concentration gradient

Question 21

Equilibrium

Answer 21

When the substance is evenly distributed.

Question 22

Lipid soluble substances that move across membranes by simple diffusion

Answer 22

Oxygen, carbon dioxide and nitrogen gases, fatty acids, steroids and fat-soluble vitamins(A, D, E and K).
Polar molecules such as water and urea also move through the lipid bilayer.

Question 23

Why is simple diffusion important?

Answer 23

The exchange of oxygen and carbon dioxide between blood and body cells and between blood and air in lungs.
Transport of lipid soluble nutrients.
The release of some waste from body cells.

Question 24

What is facilitated diffusion?

Answer 24

A passive process where an integral membrane protein assists a specific substance to move across the membrane. The protein can either be a membrane channel or a carrier.

Question 25

What is an ion channel?

Answer 25

Most membrane channels are ion channels. Ions move across the lipid bilayer down their concentration gradients. Ion channels allow a specific type of ion to move across the membrane through the channel’s pore.
E.g. In typical plasma membranes the most common ion channels are selective for K+ (potassium) or Cl- (chloride) ions.
Many ion channels are gated, a portion of it can move to open/close it.
Gated channels are important for the production of electrical signals by body cells.

Question 26

How does facilitated diffusion involving a carrier work?

Answer 26

The substance binds to a specific carrier on one side of the membrane and is released on the other after the carrier changes shape.
E.g. Glucose, fructose, galactose and some vitamins.

Question 27

How is insulin an example of the selective permeability of the plasma membrane being regulated to achieve homeostasis?

Answer 27

Insulin promotes the insertion of glucose carriers in the plasma membrane, increasing cellular glucose uptake by facilitated diffusion.

Question 28

What is osmosis?

Answer 28

A passive process in which there is net movement of water through a selectively permeable membrane.
Move from high concentration to low concentration.
Water molecules pass through plasma membranes through the lipid bilayer and through integral membrane proteins that function as water channels.

Question 29

What is osmotic pressure?

Answer 29

Pressure exerted on a membrane when a solution contains particles that cannot pass through it.
It is dependent on the concentration of the solute particles - the higher the concentration the higher the pressure.

Question 30

Why does cell volume remain the same?

What do we call a solution in which cells maintain their normal shape and volume?

Answer 30

Because the osmotic pressure cytosol and interstitial fluid is the same.
A solution where cells maintain their normal shape and volume is called an isotonic solution; there are the same concentration of impermeable solutes in the solution as in the cytosol.
E.g. A normal saline solution (0.9 percent NaCl) is isotonic for red blood cells, water molecules enter and exit the cells at the same rate so they maintain their normal shape and volume.

Question 31

What is a hypotonic solution?

Answer 31

Has a lower concentration of solutes and higher concentration of water. Water enters cells faster than it leaves causing swelling and risking it bursting.
Rupture of red blood cells is called hemolysis.

Can be used to treat dehydration.

Question 32

What is a hypertonic solution?

Answer 32

Has a higher concentration of solutes, lower concentration of water.
Water moves out faster than it moves in so the cells shrink.
Shrinkage of red blood cells is called creation.

Can be used to treat cerebral edema (excess interstitial fluid in the brain), it relieves fluid overload. As water travels by osmosis into blood.

Question 33

What is active transport?

Answer 33

An active process that moves substances across a membrane against a concentration gradient, using cellular energy

Question 34

What is ATP (Adenosine triphosphate)?

Answer 34

A nucleotide built from ribose (the sugar unit), adenine (the base) and three phosphate groups attached to the ribose.
It is sometimes called the energy currency of the body, implying that the body has to ‘earn’ / synthesise it before it can ‘spend’ it.
As the body’s reactions release energy the body captures it and uses the energy to make ATP from adenosine diphosphate (ADP).
When cells need chemical energy to fuel metabolic activities ATP is broken down into ADP, releasing water (a phosphate group) and energy from the splitting of the high energy phosphate bond.
This fuels processes including the transport of materials across membranes and muscle contraction.

Question 35

How does a protein carrier called a pump transport a substance across a cellular membrane against its concentration barrier?

Answer 35

The shape of the carrier protein (pump) changes shape using energy derived from ATP.
A typical body cell expends about 40% of its ATP on active transport.
Substances transported across the plasma membrane by active transport are mainly ions e.g. Na+, K+, H+, Ca2+, I-, and Cl-.

Question 36

What does the most important active transport pump transport?

Answer 36

It expels sodium ions Na+ from cells and brings in potassium ions K+. The pump protein also acts as an enzyme to split ATP.
This pump is called the sodium-potassium pump.
There are thousands in the plasma membrane of every cell.
Because K+ and Na+ slowly leak back across the plasma membrane down their gradients the sodium-potassium pumps must work continually to maintain low Na+ and high K+ concentrations in the cytosol.

Question 37

What is a vesicle and how does it transport substances?

Answer 37

A vesicle is a small round sac formed by budding off from an existing membrane.
It transports substance from one structure to another within cells, takes in substances from extracellular fluid and releases substances into extracellular fluid.
It is an active process because movement of the vesicles requires energy supplied by ATP.

Question 38

What are the two main types of transport in vesicles between a cell and the extracellular fluid surrounding it?

Answer 38

Endocytosis in which materials move INTO a cell in a vesicle formed from the plasma membrane.
Exocytosis in which materials move OUT of a cell by the fusion of a vesicle formed inside a cell with the plasma membrane.

Question 39

Explain phagocytosis (one type of endocytosis)?

Answer 39

Phagocytosis or ‘cell eating’ is where large, solid particles, such as whole bacteria or viruses or aged or dead cells, are taken in by the cell.
The particle binds to a plasma membrane receptor, causing the cell to extend projections of its plasma membrane and cytoplasm (called pseudopods). - two or more pseudopods surround the particle and portions of their membranes fuse to form a vesicle called a phagosome that enters the cytoplasm.- the phagosome fuses with one or more lysosomes, and lysosomal enzymes break down the ingested material. - in most cases any undigested materials remain indefinitely in a vesicle called a residual body.
Phagocytosis occurs only in phagocytes, cells that are specialised to engulf and destroy bacteria and other foreign substances. Phagocytes include certain types of white blood cells and macrophages. Phagocytosis is a vital defence mechanism that helps protect the body from disease.

Question 40

Explain bulk-phase endocytosis (a type of endocytosis a.k.a. Pinocytosis)

Answer 40

In bulk-phase endocytosis or “cell drinking” cells take up tiny droplets of extracellular fluid. This happens in most body cells and takes in the solutes dissolved in the extracellular fluid.
During this process the plasma membrane folds inward and forms a vesicle containing a droplet of intracellular fluid. This then detaches or ‘pinches off’ from the plasma membrane and enters the cytosol. Within the cell the vesicle fuses with a lysosome, where enzymes degrade the engulfed solutes. The result in smaller molecules, e.g. Amino acids and fatty acids, leave the lysosome to be used elsewhere in the cell.

Question 41

Describe exocytosis?

Answer 41

Exocytosis results in SECRETION the liberation of materials from a cell. All cells carry out exocytosis, but it is especially important in two types of cells;
- secretory cells that liberate digestive enzymes, hormones, mucus or other secretions.
- nerve cells that release substances called NEUROTRANSMITTERS via exocytosis.
During exocytosis membrane-enclosed vesicles called SECRETORY VESICLES form inside the cell, fuse with the plasma membrane and release their contents into the extracellular fluid.

Question 42

Do endocytosis and exocytosis affect the surface area of a cell’s plasma membrane?

Answer 42

No. Segments of the plasma membrane lost through endocytosis are recovered or recycled by exocytosis. The balance between the two keeps the surface area of a cell’s plasma membrane relatively constant.