2.2 All Cells Arise From Other Cells

Question 1

Cell cycle and it’s stages

Answer 1

Cycle of division with intermediate growth periods

Interphase

Nuclear division

Cytokinesis

Question 2

Why doesn’t cell cycle occur in some cells

Answer 2

Cell differentiation is when cells no longer have the ability to divide

Question 3

Diff. between cell cycle and mitosis

Answer 3

Cell cycle includes growth period between divisions

Mitosis is 10% of cycle and only refers to nuclear division

Question 4

What happens during interphase

Answer 4

G1: Cell synthesises proteins for replication

S: DNA synthesis, consists of 2 chromatids joined by centromere

G2: Organelles divide

Question 5

State purpose of mitosis

Answer 5

2 genetically identical daughter cells for:

Growth

Tissue repair

Asexual reproduxtipn

Question 6

Stages of mitosis

Answer 6

Prophase, Metaphase, Anaphase, Telophase

Question 7

What happens at Prophase

Answer 7

Chromosomes condense and become visible

Centrioles separate and move to opposite poles of cells

Spindle fibres are produced from centrioles which create a spindle apparatus from poles of cell

Spindle fibres attach to centromere and chromatids on chromosome in later stages

Question 8

Plants have a spindle apparatus but lacks…

Answer 8

Centrioles

Question 9

What happens at Metaphase

Answer 9

Chromosomes align at equator of cell

Spindle fibres releases from poles now attach to centromere and chromatid

Question 10

What happens at Anaphase

Answer 10

Spindle fibres retract and pulls centromere and chromatids towards opposite poles

Centromere divides into 2 and individual chromatids are pulled to each opposite pole

Separate chromatids = chromosomes

Question 11

What energy is used for Anaphase

Answer 11

ATP which is provided by respiration in mitochondria

Question 12

What happens at Telophase

Answer 12

Chromosomes are now at each pole of cell and become larger and thinner again

Spindle fibres disintegrates and Nucleus starts to reforms

Question 13

What happens at Cytokinesis

Answer 13

Cytoplasm splits into 2 to create 2 new genetically identical cells

Question 14

Explain root tip experiment

Answer 14

Place root in dilute HCl to halt cell division and hydrolyse middle lamella

Stain root tip with Toluidene Blue so that it binds to chromosomes

Macerate tissue in water with mounted needle

Use mounted needle at 45 to press down coverslip and obtain a single layer of cells. Avoid air bubbles

Focus an optical microscope on the slide. Count total number of cells in field of view and number of cells in a stage of mitosis

Calculate mitotic index (proportion of cells undergoing mitosis)

Question 15

Name 2 dyes that bind to chromosomes

Answer 15

Toluidene blue (blue)

Acetic orcein (purple-red)

Question 16

Why is only the root tip used when calculating a mitotic index

Answer 16

Meristematic cells at root tip are actively undergoing mitosis

Cells further away from root tip are elongating rather than dividing

Question 17

What are tumour suppressor genes

Answer 17

Genes that code for proteins to trigger apoptosis/ slows cell cycle

Question 18

What’s apoptosis

Answer 18

Programmed death of damaged cells

Question 19

What are proto oncogenes

Answer 19

Genes that code for proteins to stimulate cell cycle to progress from one stage to the next

Question 20

How can mutation to tumour suppressor genes and proto oncogenes cause cancer

Answer 20

Tumour suppressor: no production of a protein needed to slow cell cycle

Proto oncogenes: form permanently activated oncogenes

Disruption to cell cycle
|
Uncontrolled cell division
|
Tumour

Question 21

How does cancer treatment control rate of cell division

Answer 21

Disrupt cell cycle:

Prevent DNA replication

Disrupt spindle formation = inhibit Metaphase/Anaphase

Question 22

Explain binary fission

Answer 22

DNA loop replicates and stay attached at the cell membrane

Plasmids replicate in the cytoplasm

Cell membrane starts to get longer and eventually it retracts and a septum forms in the middle.

The cell has now divided into 2 with the same DNA but a variable number of plasmids

Question 23

Why are viruses classified as non living

Answer 23

Acellular: no cytoplasm, no metabolism and cannot self replicate

Question 24

Explain virus replication

Answer 24

Virus attaches to host cell membrane by attachment proteins

Injects nucleic acids via cell membrane

Cell replicates nucleic acids and produces virus particles

Question 25

2 ways in which virus leaves host cell

Answer 25

Bud off and use cell membrane to form envelope

Cause lysis of host cell

Question 26

Why’s it so difficult to develop effective treatments against viruses

Answer 26

Replicate inside living cells = difficult to kill them without killing host cell