Topic 2A: Cell Structure and Division

Question 1

Cell membrane

Answer 1

• Regulates movement of substances in and out of the cell
• Have receptors to respond to chemicals e.g. hormones

Question 2

Nucleus

Answer 2

• Nuclear envelope = double membrane with pores
• Holds chromosomes –> protein bound DNA
• Controls cell activity
• Nucleolus - makes ribosomes

Question 3

Mitochondria

Answer 3

• Double membrane –> inner folded to make cristae
• Matrix = inside the membranes = has enzymes for respiration
• Does aerobic respiration for ATP

Question 4

Chloroplast

Answer 4

• Double membrane
• Thylakoid membranes inside –> stack to make grana –> linked by lamellae (thin, flat pieces of thylakoid)
• Does photosynthesis –> some in grana, some in stroma

Question 5

Golgi apparatus

Answer 5

• Fluid filled, membrane bound, flattened sacs
• Process and package lipids and proteins

Question 6

Vesicles

Answer 6

• Smaller sacs around Golgi
• Stores lipids and proteins and transports them out of the cell

Question 7

Lysosome

Answer 7

• Type of Golgi vesicle
• Has lysozymes that digest invading cells or worn out cell parts

Question 8

Ribosome

Answer 8

• Float free or on RER
• Made of proteins and RNA
• Does protein synthesis
• Not surrounded by a membrane

Question 9

Rough Endoplasmic Reticulum

Answer 9

• System of membranes covered in ribosomes
• Folds and processes proteins made by ribosomes

Question 10

Smooth Endoplasmic Reticulum

Answer 10

• No ribosomes
• Synthesises and processes lipids

Question 11

Cell wall

Answer 11

• Cellulose in plants
• Chitin in fungi
• Supports cell and stops it changing shape

Question 12

Vacuole

Answer 12

• Contains cell sap –> sugar and salt solution
• In membrane - tonoplast
• Maintains pressure in plant cells
• Isolates unwanted chemicals

Question 13

What are prokaryotic cell walls made of?

Answer 13

Murein

Question 14

Slime capsule

Answer 14

• Protects them from attack by the immune system

Question 15

Plasmid

Answer 15

• Small DNA loops containing specific genes
• Can be passed between cells
• Not always present

Question 16

Circular DNA

Answer 16

• No nucleus –> DNA floats free

Question 17

Cytoplasm in prokaryotes

Answer 17

• Holds no membrane bound organelles

Question 18

Ribosomes in prokaryotes

Answer 18

• Much smaller than in eukaryotes
• 70s

Question 19

Flagella

Answer 19

• Long hair-like structure
• Rotates to allow the cell to move

Question 20

Describe the process of binary fission

Answer 20

• Circular DNA and plasmids replicate –> circular only once, plasmids can replicate multiple times
• Cell grows –> DNA loops move to opposite ends
• Cytoplasm begins to divide + new cell walls begin to form
• Cytoplasm divides and 2 daughter cells produced –> each has one circular DNA and a variable number of plasmids

Question 21

How are viruses structured?

Answer 21

• Core of genetic info (DNA / RNA)
• In a protein coat (capsid)
• Attachment proteins –> allow virus to attach to a host cell

Question 22

Describe virus replication

Answer 22

• Virus attach attachment proteins to complimentary receptor proteins on the host cell surface –> some viruses can only infect one type of cell
• They inject the host cell with their DNA / RNA and use its own parts to reproduce

Question 23

Define magnification

Answer 23

How much bigger an image is than the specimen

Question 24

Define resolution

Answer 24

How detailed an image is –> how easy it is to distinguish between two points

Question 25

What is the equation for magnification?

Answer 25

Magnification = image size / actual size

Question 26

Light microscopes

Answer 26

- Use light to form an image - Max resolution = 0.2 micrometres --> can see nucleus - Max mag = x1500 - Can view live specimens - Can see in colour

Question 27

Electron microscopes

Answer 27

- Use electrons to form an image - Higher resolution --> 0.0002 micrometres - Max mag = 1,500,000 - Black and white images only - Specimens must be dead

Question 28

Transmission Electron Microscopes

Answer 28

- Transmit a beam of electrons through the sample - Denser parts absorb more --> look darker - Has high resolution --> can see internal structure of organelles - Can only be used on thin specimens

Question 29

Scanning Electron Microscopes

Answer 29

- Scan a beam of electrons over specimen knocking off electrons from the specimen --> collected in cathode ray tube to make the image - 3D image - Can be used on thicker specimens - Lower resolution

Question 30

What are microscope artefacts?

Answer 30

- Things you can see down a microscope that are not parts of the cell e.g. fingerprints, bubbles, dust

Question 31

Describe homogenisation and conditions needed

Answer 31

- Vibrate or grind cells to break membrane and release organelles - Ice cold --> reduces enzyme activity to stop organelles being broken down - Isotonic --> same conc in and out to prevent damage to organelles by osmosis - Buffer solution --> maintains pH

Question 32

Desrcibe filtration of cell components

Answer 32

- Filtered through a gauze to remove large cell / tissue debris

Question 33

Describe ultracentrifugation

Answer 33

- Cell fragments in solution spun in centrifuge - Heaviest organelles flung to the bottom = pellet - Suspended organelles = supernatant - Supernatant drained off + spun again - Repeated to separate all organelles - Nuclei, chloroplasts (if present), mitochondria, lysosomes, RER + SER, ribosomes

Question 34

Describe interphase

Answer 34

- G1= cell grows and new proteins and organelles are made - S = DNA replicates - G2 = cell keeps growing + proteins needed for mitosis are made

Question 35

What is mitosis used for?

Answer 35

Growth and repair

Question 36

Describe the stages of mitosis

Answer 36

- Prophase --> chromosomes condense, centrioles move to opposite ends and form spindles, nuclear envelope breaks down - Metaphase --> Chromosomes line up down the middle + spindles attach to centromere - Anaphase --> Centromeres divide and sister chromatids separate, spindles contract pulling chromatids to opposite ends - Telophase --> Sets of chromosomes collect at opposite ends, new nuclear membranes form, chromosomes become long and thin again, cytoplasm divides

Question 37

What is cancer?

Answer 37

- Uncontrolled cell growth due to a gene mutation - Cell division stops responding to normal regulations so cells rapidly divide - Cells clump to form tumours

Question 38

What are benign tumours?

Answer 38

- Divide at a normal rate, don't invade other tissues - Usually harmless but can press on other organs and impact their function - If needed they can be surgically removed

Question 39

What are malignant tumours?

Answer 39

- Divide rapidly and interfere with organ functions - Invade other tissues via metastasis - Parts can break off and travel round the body to form secondary growths making it very harmful and difficult to treat

Question 40

What are come causes of cancer?

Answer 40

- Genetics e.g. BRCA1+2 - Radiation exposure --> including UV - Substances e.g. smoking, alcohol

Question 41

What are some treatments for cancer?

Answer 41

- Chemotherapy --> prevents synthesis of enzymes needed in DNA replication to stop the cell cycle --> usually drugs that target quick dividing cells - Radiotherapy --> can damage DNA so it doesn't make it past checkpoints preventing cell cycle - Surgery - Drugs --> can prevent spindle fibres forming to prevent mitosis

Question 42

Describe the root tip squash practical.

Answer 42

- Cut 1cm tip off the root - Put HCl in a test tube in a water bath at 60 degrees - Put the tip in the acid and leave for 5 mins - Pipette rinse the tip with water and dry - Cut 2mm of the tip off and put on a microscope slide - Use a mounted needle to break the tip open and spread the cells thinly - Add a stain to make the chromosomes easier to see - Place a cover slip over and push down on top to squash the tissue - Observe with a microscope

Question 43

What is the calculation for mitotic index?

Answer 43

mitotic index = number of cells with visible chromosomes / total number of cells observed