Cell Biology (and cell cycle)

Question 1

What is the function of the nucleus?

Answer 1

• Contains genetic information in the form of chromosomes (made of DNA)
• control centre of the cell
• produces mRNA, the blueprint for photo synthesis

Question 2

Where in the nucleus is rRNA manufactured?

Answer 2

Nucleolus

Question 3

What is the nuclear envelope?

Answer 3

Double membrane surrounding the nucleus controlling what enter and leaves the cell. It has gaps inside it called nuclear pores to allow large molecules to leave.

Question 4

What is the chromatin in the nucleus?

Answer 4

DNA organised into chromosomes which unravel and diffuse when the cell is not dividing.

Question 5

Which part of the nucleus makes up most of that cell?

Answer 5

Nucleoplasm, jelly-like material

Question 6

Explain the difference between sER and rER

Answer 6

Smooth endoplasmic reticulum - makes and processes lipids
Rough endoplasmic reticulum - processes proteins made at the ribosomes.

Question 7

What is the Endoplasmic Reticulum? (ER)

Answer 7

System of membrane bound tubes called cisternae spread through the cytoplasm, usually joining from the nucleus. Provides large surface area for protein synthesis and glycoproteins. Transports particular proteins through the cell.

Question 8

What are the two types of ribosomes?

Answer 8

80S and 70S. 80S are larger cells, found in eukaryotic cells. 70S are smaller in diameter and are found in prokaryotic cells.

Question 9

Describe the structure and function of a mitochondrion

Answer 9

Contains a double membrane, outer and inner. The cristae is the folding of the inner membrane to provide a larger surface area for some respiration enzymes to attach to. The matrix is the material inside the inner membrane containing DNA, proteins, lipids and some enzymes. Mitochondria produces energy carrier ATP as it is the site of aerobic respiration

Question 10

What is the function of lysosomes?

Answer 10

Contains hydrolytic enzymes (breaking-down enzymes)
• formed by the Golgi. Contains proteases and lipases so they don’t damage rest of the cell.
• breaks down worn out organelles to recycle their parts, and material ingested by phagocytic cells.

Question 11

How do lysosomes release enzymes?

Answer 11

Exocytosis

Question 12

What is the function of the Golgi apparatus?

Answer 12

Produces enzymes, creates glycoproteins (adding carbohydrates to some proteins), modifies, processes and packages proteins and lipids made in the ER and transports them off to the correct part if the cell in vesicles.

Question 13

What is the function of the cell membrane?

Answer 13

Surrounds the cells and controls what goes in and out of the cell based on size and charge. Made up of lipids and proteins. Folded into finger-like projections called microvilli which increase the surface are of the membrane.

Question 14

What three organelles are found in plant cells only?

Answer 14

Chloroplasts, call wall and permanent vacuole.

Question 15

Describe the permanent vacuole and its function

Answer 15

Taking up to 90% of a plant cells volume, it contains a solution of mineral salts, sugars, amino acids and wastes.
Maintains pressure inside the cell and keeps it rigid to help stop plant wilting

Question 16

What is a prokaryotic cell wall made of?

Answer 16

Peptidoglycan (not cellulose like it is in eukaryotic cells)

Question 17

What does the slime capsule surrounding the bacteria cell do?

Answer 17

Protect bacteria from attack by cells from the immune system

Question 18

What three structures do only some prokaryotic cells have and what do they do?

Answer 18

•Flagella/pilus on the end of the cell that plays an important role in bacterial conjugation
•capsule of slime to protect the cell from attack from immunal cells
•plasmid DNA in cells that contain genes for antibiotic resistance. This can be additional to the DNA that floats free in the cytoplasm

Question 19

Describe what binary fission is and the process of it.

Answer 19

Binary fission is the process by which prokaryotic cells divide. It involves:
1. Cell replicates its DNA and plasmids
2. The cytoplasmic membrane elongates, separating DNA molecules to opposite poles.
3. Cross wall forms forms, membrane starts to split.
4. Cross wall forms completely and cytoplasm divides.
5. Two daughter cells are produced. Each daughter cell has one copy of the circular DNA but can have varied number of copies of plasmid.

Question 20

How do viruses vary from prokaryotic cells?

Answer 20

• varying structure.
• acellular - not actually cells. They are nucleic acid surrounded by protective protein coat called a capsid.
  •they do not undergo cell division as they are not alive. Instead they inject their DNA into the host cell.

Question 21

What is resolution?

Answer 21

The degree of detail that can be seen. How well a microscope can distinguish between two points.

Question 22

What is magnification?

Answer 22

Number of times larger an image is that the specimen.
Magnification = image size / actual size.

Question 23

Compare optical microscopes (light) with electron microscopes.

Answer 23

Electron microscopes have much higher magnification and much higher resolution as electron beam has a shorter wavelength. (This allows for smaller structures to be seen)

Question 24

Define and compare SEMs and TEMs

Answer 24

TEMs:
•Transmission electron microscopes use electron microscopes to focus a beam of electrons through the specimen.
•Denser parts of the specimen appear darker as they absorb more electrons.
•2D and are used on thin, non living specimens as they are put into a vacuum.
• higher resolution as the electrons have a shorter wavelength.
•shows structure of internal organelles
SEMs:
•can a beam of electrons across the specimen.
• can be 3D and used on thick specimens
• only used on non living specimens
•lower resolution.

Question 25

Describe the steps for a temporary mount.

Answer 25

1. Using a pipett, put a small drop of water on the centre of the slide. 2. Using tweezers, place the specimen on the water drop (thin slice) 3. Add a drop of stain to highlight parts of the cell e.g iodine to highlight starch. 4. Add glass cover slip to protect. Avoid air bubbles as they can obstruct view to specimen.

Question 26

What is homogenisation?

Answer 26

Breaking up the cell. This can be done by vibrating them or breaking up in a blender. This breaks up the plasma membrane and releases organelles into a solution. Important, because organelles need to be released to be examined.

Question 27

What conditions must the solution be that holds the broken cell? (Organelles)

Answer 27

Ice cold solution to reduce enzyme activity that breaks down organelles. Isotonic solution to prevent damage to the organelles through osmosis. Buffer solution added to maintain pH.

Question 28

What is involved in the filtration step of cell fractionation?

Answer 28

Filtering the solution through a gauze to separate large cell debris or tissue debris like connective tissue. Important to only get organelles examined and not confused with unwanted debris.

Question 29

What is ultracentrifugation?

Answer 29

The process of separating organelles based off size and density. The fragments are put into a tube and spun in a centrifuge. Firstly on a low speed to separate the heaviest organelles. (Nucleus) forming a thick sediment at the bottom called a pellet. The rest of the organelles stay suspended in the fluid above, called the supernatant). This is drained off and put into another tube and spun at a slightly higher speed. Next the mitochondria would be removed. This is repeated until all organelles are separated in order of mass with ribosomes being last.

Question 30

What is the prophase stage of mitosis?

Answer 30

Chromosomes condense becoming short and fatter more visible. Centrioles move apart and towards the poles of the cell The spindle (network of protein fibres) begin to form Nuclear envelope and nucleolus disappear so chromosomes lie free

Question 31

What happens in the metaphase stage of mitosis?

Answer 31

Chromosomes move to the middle of the cell and attach to the spindle via their centromere. Centrioles move to opposite ends of cell (METAPHASE = MIDDLE)

Question 32

What happens in the anaphase stage of mitosis?

Answer 32

Spindle fibres contract and pull the two chromatids of each chromosome to opposite poles of the cell. ANAPHASE = APART

Question 33

What happens in the telophase of mitosis?

Answer 33

The chromosomes become long and thin again as they start to unwind A new nuclear envelope forms around each nucleus The spindle fibres disappear The cytokinesis occurs where the cytoplasm divides to form two new cells.

Question 34

What happens in the interphase of mitosis?

Answer 34

DNA unravelled and replicated to double its genetic content. Organelles are replicated ATP content is increased to provide energy for division.

Question 35

What is cancer?

Answer 35

A tumour that invades surrounding tissue. They are formed by uncontrollable division of cells usually if there’s a mutation in a gene that controls cell division.

Question 36

What is a microscope artefact? Give an example.

Answer 36

Things you can see through the microscope that aren’t part of the specimen you’re looking at. For example, dust, air bubbles, fingerprints.

Question 37

How do you know if what you’re looking at has an artefact?

Answer 37

If an object can be seen with one preparation technique but not another. This is because they are made during preparation and shouldn’t be there.

Question 38

Describe how viral replication takes place.

Answer 38

Viruses attachment proteins attach to the host cells receptor proteins. Genetic material is released into the cell The genetic material is replicated by the host cells receptor proteins Viral components assemble Replicated viruses release from host cells

Question 39

Describe the structure of a chloroplast

Answer 39

Double membrane, flattened disc shape Small membrane inside called thylakoid membrane containing chlorophyll. These are stacked to form grana and are joined by lamella which are flattened pieces of thylakoid membrane. Stroma - contains starch grains, ribosomes and DNA.

Question 40

What is the function of a chloroplast?

Answer 40

Site of photosynthesis

Question 41

Cell wall function

Answer 41

Supports the cell and prevents changing shape. Made of cellulose.

Question 42

What are cell walls made of in fungal cells?

Answer 42

Chitin

Question 43

Function of a mitochondria

Answer 43

Sure of aerobic respiration. Produces ATP

Question 44

Function of permanent vacuole

Answer 44

Keep cell rigid and stops plants wilting. Can also isolate unwanted chemicals in the cell.

Question 45

Why should students soak root tips in hydrochloric acid? (Practical on mitotic index calculation)

Answer 45

It breaks down the links in the cell wall To allow cells to be easily squashed

Question 46

How is the mitotic index calculated?

Answer 46

Cell in mitosis divided by total amount of cells in field of view

Question 47

Why does the coverslip enable students to see mitosis clearly? (Practical on mitotic index)

Answer 47

It is pressed down to create a thin layer of cells and spread them out so light can pass through.

Question 48

Why may students calculate different mitotic indicies from following the same method?

Answer 48

• different parts of the root tip will have different fields of view. • roots will go through mitosis and different times.

Question 49

Why are cells taken from the root tip?

Answer 49

To have a region where mitosis occurs.