Topic 2 - Cells

Question 1

Outline the cell theory

Answer 1

1. All living organisms are composed of cells
2. Cells are the smallest unit of life
3. Cells only come from pre-existing cells

Question 2

What are the evidence for the cell theory?

Answer 2

1. Cell organelles cannot survive outside of the cell
2. Observations of cells during division
3. Spontaneous generation of life from biological organisms smaller than cells is impossible

Question 3

What are the functions of life unicellular organisms carry?

Answer 3

1. Metabolism
2. Response
3. Homeostasis
4. Growth
5. Reproduction
6. Nutrition

Question 4

What are the relative sizes of molecules, cell membranes, viruses, bacteria, organelles, and cells?

Answer 4

• molecules 1 nm
• thickness of cell membranes 10 nm
• viruses 100 nm
• bacteria 1 µm
• organelles up to 10 µm
• most cells up to 100 µm

Question 5

Explain the importance of the surface area to volume ratio as a factor limiting cell size

Answer 5

The rate of heat/waste production and resource consumption of a cell is proportional to itse volume, whereas the rate of exchange of materials and energy (heat) is proportional to its surface area. Thus, cells with more surface area per unit volume are able to move more materials in and out of the cell.

Question 6

Do multicellular organisms show emergent properties?

Answer 6

Yes.

Question 7

How do cells differentiate to carry out specialised functions?

Answer 7

They express some of their genes but not others, thus making every cell specialised to its action.

Question 8

How are stem cells different from regular cells?

Answer 8

They retain the capacity to divide and have the ability to differentiate along different pathways to any kind of cell.

Question 9

Outline the therapeutic use of stem cells

Answer 9

1. Parkinson’s and Alzheimer’s diseases by replacing dead brain cells
2. Diabetes by replacing malfunctional pancreatic cells to produce insuln
3. Tissue-specific stem cells that can be used to regrow different tissues around the body

Question 10

Draw and label a diagram of a prokaryote

Answer 10

Question 11

What is the function of a prokaryotic cell wall and what is it made of?

Answer 11

It protects and maintains the shape of the cell. It is composed of a carbohydrate-protein called peptidoglycan. Some bacteria have an additional layer of polysaccharide which makes the bacterium possible to adhere to teeth, skin, and food.

Question 12

What is the function of a plasma membrane?

Answer 12

It controls the movement of materials in and out of the cell and plays a role in binary fission.

Question 13

What is the function of cell cytoplasm?

Answer 13

It occupies the complete interior of the cell and cellular processes occur in it.

Question 14

What is the function of pili?

Answer 14

They are used for attachment, for example in joining bacteria in the transfer of DNA.

Question 15

What are flagella?

Answer 15

They allow cell motility in prokaryotes.

Question 16

What are ribosomes?

Answer 16

Sites of protein synthesis.

Question 17

What is a nucleoid?

Answer 17

Controls a prokaryotic cell and reproduction. (Contains naked DNA)

Question 18

What is binary fission and what happens during it?

Answer 18

Prokaryotic cells’ way of dividing. The DNA is copied, the two daughter chromosomes attach to opposite sides, and the cell divides into two.

Question 19

Draw and label a diagram of an animal cell

Answer 19

Question 20

What is the function of free ribosomes, where are they found, and what are they composed of?

Answer 20

They carry out protein synthesis and are found either in the cytoplasm or attached to rough ER. They are made of RNA and protein. NB: ribosomes of eukaryotic cells are larger and denser than of prokaryotic cells.

Question 21

What is endoplasmic reticulum (ER)?

Answer 21

An extensive network of tubules and channels that extend almost everywhere in the cell.

Question 22

What is rough endoplasmic reticulum (rER)?

Answer 22

Usually located near the nuclear membrane. Its structure enables transportation of materials. Ribosomes are attached to the surface of rER.

Question 23

What is smooth endoplasmic reticulum (sER)?

Answer 23

Tubules that have different enzymes on its surface. Functions include:

• production of membrane phospholipids and cellular lipids
• production of sex hormones
• detoxification of drugs (in the liver)
• storage of calcium ions
• transportation of lipid-based compounds
• aid the liver in releasing glucose

Question 24

What are lysosomes and where do they come from?

Answer 24

Structures that lack internal structures that arise from Golgi. Fuse with old and damaged organelles within the cell to recycle nutrients. Also takes part in phagocytosis.

Question 25

What is Golgi apparatus and its sides?

Answer 25

Carries out collection, packaging, modification, and distribution of materials synthesised in the cell. Cis side receives products from rER and trans side sends off materials in vesicles. Very important in glandular cells.

Question 26

Describe mitochondria

Answer 26

They have their own DNA. Have a double membrane, smooth on the outer side and folded (cristae) on the inner side. Cristae provide large surface area. Inside of the organelle is filled with matrix. Produces ATP. Also produces and contains its own ribosomes.

Question 27

Describe the nucleus

Answer 27

Basically controls the cell and without it the cell cannot reproduce. Contains DNA in the nucleolus. Produces ribosomes in the nucleolus.

Question 28

Describe chloroplasts

Answer 28

Very similar to mitochondria. Double membrane, contains its own DNA, includes grana, thylakoids, and stroma. Granum = stack of thylakoids, thylakoid = absorbs sunlight, stroma = the fluid inside

Question 29

What are vacuoles?

Answer 29

Storage organelles that are included in the transport of nutrients.

Question 30

Compare prokaryotic and eukaryotic cells

Answer 30

naked DNA VS nucleus free DNA VS enclosed DNA no mitochondria VS yes mitochondria 70S ribosomes VS 80S ribosomes no internal compartmentalisation VS organelles in eukaryotes

Question 31

Compare plant cells and animal cells

Answer 31

maintained shape VS random shape cell wall VS no cell wall chloroplasts VS no chloroplasts store starch VS store glycogen

Question 32

Outline two roles of extracellular components

Answer 32

The plant cell wall maintains the cell shape, prevents excessive water intake, and holds the whole plant up against gravity. Animal cells secrete glycoproteins that form the extracellular matrix, which functions in support, adhesion (cell-to-cell interaction), and movement.

Question 33

Draw and label a diagram of the structure of a membrane

Answer 33

Integral proteins completely prenetrate the bilayer (control entry and removal of molecules from the cell) Peripheral proteins attached to the surface Cholesterol helps to regulate membrane fluidity and stability Glycoproteins attached to peripheral proteins recognise similar cells and are involved in immune responses

Question 34

How do the hydrophobic and hydrophilic properties of phospholipids help to maintain the structure of cell membranes?

Answer 34

The properties cause the phospholipids to always align as a bilayer if there is water present. The phobic tail is repelled and therefore points inwards whereas the philic head is attracted and points outwards, forming a bilayer. The tails don't strongly attract each other making the membrane fluid and flexible. This allows anymal cells to have a variable shape.

Question 35

List the functions of membrane proteins

Answer 35

1. Hormone binding sites - cells have specific shapes that fit the hormone and attachment causes a change in shape 2. Enzymatic action - catalyse chemical reactions 3. Cell adhesion - glycoproteins hook together 4. Cell-to-cell communication - glycoproteins 5. Channels for passive transport 6. Pumps for active transport

Question 36

What is diffusion?

Answer 36

The passive movement of particles from a region of high concentration to a region of low concentration

Question 37

What is osmosis?

Answer 37

The passive movement of **water** molecules, across a partially permeable membrane, from a region of lower concentration to a region of higher concentration.

Question 38

Explain passive transport across membranes by simple diffusion

Answer 38

Particles move from a region of high concentration to a region of low concentration

Question 39

Explain passive transport across membranes by facilitated diffusion

Answer 39

Involves a membrane with specific carrier proteins that are capable of combining with the substance to aid its movement. The rate will level off when total saturation occurs.

Question 40

Explain the steps of active transport with protein pumps (sodium-potassium)

Answer 40

1. Protein binds to three Na ions 2. Binding causes phosphorylation and ATP attaches to the protein 3. Phosphorylation causes protein to change shape, thus expelling sodium ions. ADP is released and one phosphate remains 4. Two K ions bind to the other site of the protein. This releases the phosphate group 5. Loss of phosphate restores protein's original shape and K ions are released to intracellular space

Question 41

Explain endocytosis

Answer 41

Endocytosis is the intake of macromolecules. The plasma membrane pinches off to enclose macromolecules into a vesicle. The ends of the plasma membrane reattach due to hydrophobic and philic properties. Examples include phagocytosis and pinocytosis (intake of extracellular fluids).

Question 42

Explain exocytosis and its steps

Answer 42

Essentially the reverse of endocytosis. Usually begins in the ribosomes of rER. There are four steps: 1. Protein produced by ribosomes enters the lumen of rER. 2. Protein exits the ER and enters the cis side of Golgi in a vesicle. 3. The protein is modified in Golgi and exits on the trans side inside another vesicle. 4. The vesicle fuses with the plasma membrane → secretion of the contents Examples include pancreas cells producing insulin and neurotransmitters released at the synapses.

Question 43

List the stages in the cell cycle

Answer 43

1. Interphase (G₁, S, G₂) 2. Mitosis 3. Cytokinesis

Question 44

Describe interphase

Answer 44

Composed of three major stages - G1 = growth of the cell, - S = replication of the DNA, increase in no. of mitochondria and/or chloroplasts - G2 = cell growth and preparation for mitosis (organelles increase, DNA begins to condense, microtubules begin to form)

Question 45

What are tumours the result of?

Answer 45

Uncontrolled cell division. Can occur in any organ or tissue.

Question 46

List the stages of mitosis

Answer 46

(interphase) 1. Prophase 2. Metaphase 3. Anaphase 4. Telophase

Question 47

Explain what happens in mitotic prophase

Answer 47

1. Chromatin becomes more tightly coiled to form chromosomes 2. Nuclear envelope disintegrates and nucleoli dissappear 3. Mitotic spindle begins to form and is complete at the end of prophase 4. Centromeres attach to the spindle fibres 5. Centrosomes move toward opposite poles

Question 48

Explain what happens in mitotic metaphase

Answer 48

1. Chromosomes are aligned at the equator of the cell 2. Centrosomes are at opposite poles

Question 49

Explain what happens in mitotic anaphase

Answer 49

1. Centromeres divide into two and the chromatids become **chromosomes** 2. Chromosomes move toward opposite poles of the cell by shortening microtubules 3. Chromosomes move centromeres first because they are the ones attached to the centrosomes

Question 50

Explain what happens in mitotic telophase

Answer 50

1. All chromosomes have arrived at the poles of the cell 2. Nuclear envelopes begin to form 3. Chromosomes start to form chromatin and nucleoli reappear