1
Q
What is the cell cycle?
A
An ordered sequence of events that takes place in cells, resulting in division of the cell, and the formation of two genetically identical daughter cells.
2
Q
Explain interphase.
A
- cells do not divide continuously.
- it is a long period of growth and carrying out separate functions. Cell spends majority of its time in this phase.
- takes place between devisions. (Not a stage in division).
During interphase: - dna replicated + checked for errors in nucleus.
- protein synthesis occurs in cytoplasm.
- mitochondria grow + divide.
- chloroplasts grow + divide (in plant cells).
- normal metabolic processes occur (e.g respiration).
3
Q
What are the 3 stages of interphase?
A
G1- first growth phase. Proteins from which organelles are synthesised are produced. Organelles replicate. Cell increases in size.
S- synthesis phase. Dna replicated in nucleus.
G2- second growth phase- cell continues to increase in size, energy stores increased. Duplicated dna checked for errors.
4
Q
What is the mitotic phase?
A
The period of cell devision. Has 2 stages:
- Mitosis- nucleus divides.
- Cytokinesis- cytoplasm divides to form 2 cells.
5
Q
What is G0 ?
A
The phase where the cell leaves the cycle, either temporarily or permanently.
Reasons for this:
1. differentiation- cell becomes specialised to a particular function and is no longer able to divide.
2. DNA may be damaged- a damaged cell cannot divide and enters a period of permanent cell arrest (G0).
3. As you age, the number of cells in your body increases. Growing numbers of senescent cells have been linked to diseases (cancer/arthritis).
Some cell types that enter G0 can be stimulated to go back to cell cycle and divide again. (Eg. Lymphocytes)
6
Q
What must be controlled about the cell cycle?
A
It is vital to ensure that the cell only divides when:
- it has grown to the right size.
- the replicated dna is error free.
- chromosomes are in their correct positions (during mitosis).
This ensures the fidelity of cell division- that 2 daughter cells are created from the parent cell.
7
Q
What are check points?
A
The control mechanisms of the cell cycle.
Monitor and verify whether processes at each stage have been completed accurately before progressing to next stage.
8
Q
What is the first checkpoint and its role?
A
G1 checkpoint:
- checkpoint at the end of G1 phase (before S phase).
- checks for; cell size, nutrients, growth factors, dna damage.
- if these are satisfied it triggers dna replication. If not it enter G0 (resting state).
9
Q
What is the second checkpoint and its role?
A
G2 checkpoint:
- the checkpoint at the end of G2 phase. Before the start of mitotic phase.
- checks for; cell size, dna replication (without error), dna damage.
- if these are satisfied, cell initiates the molecular processes that signal the start of mitosis.
10
Q
What is the final checkpoint?
A
Spindle assembly/metaphase checkpoint:
- at the metaphase stage of mitosis.
- checked for chromosomes to be attached to spindle fibres.
- mitosis can’t proceed until this is passed.
11
Q
What is mitosis and its importance?
A
Mitosis is the entire process of cell devision in eukaryotic cells.
- refers to the division of the nucleus.
- ensures that both daughter cells produced are genetically identical, have an exact copy of the dna present in the parent cell and the same number of chromosomes.
- necessary for growth, replacement and repair of tissues in multicellular organisms as daughter cells have to be identical.
- also necessary for asexual reproduction.
12
Q
What is asexual reproduction?
A
Production of genetically identical off spring from one parent in multicellular organisms such as plants, fungi and some animals. Also in single celled organisms.
Bacteria don’t have a nucleus so reproduce asexually by binary fission.
13
Q
What are chromatids and the centromere?
A
When dna in the nucleus is replicated during interphase, each chromosome is converted into 2 identical dna molecules called chromatids.
The two chromatids are joined together at a region called the centromere. It is necessary to keep the chromatids together during mitosis so they can be precisely manoeuvred and segregated equally, one each into 2 new daughter cells.
14
Q
What are the 4 stages of mitosis and how can they be viewed?
A
Prophase, metaphase, anaphase, telophase.
They flow seamlessly from one to another.
- can be viewed and identified using a light microscope.
- dividing cells easily obtained from growing root tips of plants. They can be treated with a chemical to allow cells to be separated and then squashed.
- stains that bind to dna used to make chromosomes clearly visible.
15
Q
Explain prophase.
A
- Chromatin fibres begin to coil and condense to form chromosomes. Nucleolus disappears. Nuclear membrane starts to break down.
- Protein microtubules form spindle- shaped structures linking the poles of the cell. Fibres forming spindle are necessary to move chromosomes into correct positions before division.
- Two centrioles migrate to opposite poles of the cell. (In animals/some plants).
- Spindle fibres attach to specific areas on the centromeres and move chromosomes to the centre.
- By the end, nuclear envelope has disappeared.
16
Q
Explain metaphase?
A
- chromosomes are moved by the spindle fibres to form a plane in the centre of the cell, called the metaphase plate, and then held in position.
17
Q
explain anaphase.
A
- centromeres holding together the pairs of chromatids in each chromosome divide during anaphase.
- chromatids are separated by being pulled to opposite poles by the shortening spindle fibres.
- ‘V’ shape of chromatids is because they are dragged by their centromeres through the liquid cytosol.
18
Q
Explain telophase.
A
- the chromatids have reached the poles and are now called chromosomes.
- the 2 new sets of chromosomes assemble at each pole.
- nuclear envelope reforms around them.
- chromosomes start to uncoil, nucleolus formed.
- cytokinesis begins.
19
Q
What is cytokinesis?
A
The actual division of the cell into two separate cells.
Begins during telophase.
20
Q
Explain cytokinesis in animal cells.
A
- a cleavage furrow forms around the middle of the cell.
- cell surface membrane pulled inwards by the cytoskeleton until it is close enough to fuse around the middle, forming two new cells.
21
Q
Explain cytokinesis in plant cells.
A
have cell walls so formation of cleavage furrow not possible.
- vesicles from the Golgi apparatus assemble in the same place as the metaphase plate.
- vesicles fuse with each other and the cell surface membrane, dividing the cell in 2.
- new sections of cell wall form along the new membrane sections.
- (if cell wall is formed before the daughter cells separated, they would immediately undergo osmotic lysis from the surrounding water.)
22
Q
What is meant by the terms diploid, gametes, zygote?
A
Diploid - the normal chromosome number: Normal cells have 2 chromosomes of each type. One from each parent.
In sexual reproduction, two sex cells (gametes) fuse to produce a fertilised egg (zygote).
Gametes must contain half the standard (diploid) number of chromosomes.
23
Q
Explain through which process gametes are formed.
A
Gametes are formed by another form of cell division called meiosis.
- the nucleus divides twice to form 4 daughter cells= the gametes.
- each gamete contains half of the chromosome number of the parent cell. It is haploid.
- meiosis is therefore known as reduction division.
24
Q
What are homologous chromosomes?
A
Each nucleus contains matching sets of chromosomes, called homologous chromosomes, and is termed a diploid.
- each chromosome in a homologous pair has the same genes at the same loci.
- as homologous chromosomes have the same genes in the same positions, they will be the same size and length once visible in prophase. Centromeres will also be in the same positions.
25
What are alleles?
Different versions of the same gene.
| The different alleles of a gene will have the same locus (position on particular chromosome)
26
What are the stages of meiosis?
involves 2 divisions:
1. Meiosis I - the reduction division when the pairs of homologous chromosomes are separated into 2 cells. The cells are haploid as each new cell will only contain one full set of genes instead of two.
2. Meiosis II - the pairs of chromatids present in the daughter cells are separated to form 2 more cells.
4 haploid daughter cells produced in total.
27
Explain prophase 1 (meiosis).
- chromosomes condense.
- nuclear envelope disintegrates.
- nucleolus disappears.
- spindle formation begins.
- homologous chromosomes pair up, forming bivalents.
- crossing over occurs as chromosomes are large and chromatids entangle whilst moving through the liquid cytoplasm.
28
Explain metaphase 1.
- homologous pairs of chromosomes assemble along the metaphase plate.
- orientation of each homologous pair on the metaphase plate is random and independent.
- independent assortment = maternal/paternal chromosomes end up facing either pole resulting in different combinations of alleles. This results in genetic variation.
29
Explain anaphase 1.
- homologous chromosomes are pulled to opposite poles and chromatids stay joined together.
- sections of dna on ‘sister’ chromatids which entangled during cross over, break off and rejoin. Sometimes dna is exchanged as a result.
Points at which the chromatids break and rejoin = chiasmata.
- the exchange forms recombinant chromatids. Combination of alleles on them will be different from combination on original chromatids.
- genetic variation rises from new combination. Sister chromatids = no longer identical.
30
Explain telophase 1.
- chromosomes assemble at each pole.
- nuclear membrane reforms.
- chromosomes uncoil.
- cell undergoes cytokinesis and divides into 2 cells.
- reduction of chromosome number from diploid to haploid is complete.
31
Explain prophase 2.
- chromosomes(still consisting of 2 chromatids) condense and become visible again.
- nuclear envelope breaks down.
- spindle formation begins.
32
Metaphase 2.
- individual chromosomes assemble on the metaphase plate.
| - due to crossing over, the chromatids are no longer identical = independent assortment again = more genetic variation.
33
Anaphase 2.
- chromatids of individual chromosomes are pulled to opposite poles after division of the centromeres.
same as mitosis anaphase.
34
Telophase 2.
- chromatids assemble at the poles.
- chromosomes uncoil and form chromatin again.
- nuclear envelope reforms.
- nucleolus becomes visible.
- cytokinesis results in division forming 4 daughter cells.
Cells haploid due to reduction division.
Cells are genetically different to eachother + parent cell due to crossing over/independent assortment.
35
What are the levels of organisation in multicellular organisms?
Specialised cells = tissues = organs = organ systems = whole organism.
36
how are erythrocytes specialised.
Erythrocytes/ red blood cells:
1. flattened biconcave shape- increases SA to V ratio. Essential to their role of transporting oxygen around body.
2. In mammals, don’t have a nuclei- increases space available for haemoglobin .
3. Flexible- able to squeeze through narrow capillaries.
37
how are neutrophils specialised?
Neutrophils are a type of white blood cell. Play an essential role in immune system.
1. Multi-lobed nucleus - makes it easier to squeeze through small gaps to get to infections.
2. Granular cytoplasm contains many lysosomes that contain enzyme used to attack pathogens.
38
How are sperm cells specialised?
Sperm cells = male gametes. Deliver genetic info to female gamete.
1. Flagellum- aids movement.
2. Many mitochondria- supplies energy needed to swim.
3. Acrosome on head - contains digestive enzymes to break through protective layers around ovum and allow sperm to penetrate.
39
How are palisade cells specialised?
Present in the mesophyll.
1. chloroplasts- absorb large amounts of light for photosynthesis.
2. Cells are rectangular shapes - can be closely packed to form continuous layer.
3. Thin cell walls - increases rate of diffusion of co2.
4. Large vacuole- maintains turgor pressure.
5. Chloroplasts can move in cytoplasm to absorb more light.
40
How are root hair cells specialised?
Present at the surfaces on roots near the growing tips.
| 1. Long extensions called root hairs- increase surface area. This maximises uptake of water and minerals from soil.
41
How are guard cells specialised?
Pairs of guard cells on the surfaces of leaves form small openings called stomata which are necessary for co2 to enter plants for photosynthesis.
1. When guard cells lose water and become less swollen, stomata closes to prevent further water loss.
2. Cell wall is thicker on one side- so cell doesn’t change shape symmetrically as its volume changes.
42
What is a tissue?
A tissue is made up of a collection of differentiated cells that have specialised functions. As a result each tissue is adapted for a a particular function within organisms.
43
What are the 4 main categories of tissue in animals and their adaption.
1. Nervous tissue- support transmission of electrical impulses.
2. Epithelial tissue- to cover internal and external body surfaces.
3. Muscle tissue- to contract.
4. Connective tissue- either to hold tissue together or as a transport medium.
44
Squamous epithelium.
specialised tissue made up of specialised squamous epithelial cells. Flat appearance .
1. Very thin due to the flat cells that it consists of. Only one cell thick.
2. Present when rapid diffusion across a surface is essential.
3. Forms lining of the lungs and allows rapid diffusion of oxygen into blood.
45
Ciliated epithelium.
Specialised tissue made up of ciliated epithelial cells.
1. Cells have hair like structures called cilia on one surface that move in rhythmic manner.
2. Ciliated epithelium lines the trachea- causes mucus to be swept away from lungs.
3. Goblet cells present - release mucus to trap any unwanted particles present. Prevents bacteria reaching alveoli.
46
Cartilage.
Connective tissue found in outer ear, nose, ends (and between) of bones.
1. Contains fibres of proteins elastin and collagen. Firm + flexible.
2. Composed of chondrocyte cells embedded in an extra cellular matrix.
3. Cartilage prevents bones rubbing together and causing damage.
47
Muscle.
A tissue that needs to be able to shorten in length in order to move bones.
1. Skeletal muscle fibres contain myofibrils which contain contractile proteins.
48
Epidermis
A single layer of closely packed cells covering the surfaces of plants.
1. covered by waxy, waterproof cuticle - reduces water loss.
2. Presence of stomata- allow co2 and oxygen in and out.
49
Phloem tissue.
Type of vascular tissue in plants. Responsible for transport of organic nutrients (sucrose) from leaves and stems.
1. Composed of columns of sieve tube cells separated by perforated walls called sieve plates.
50
What is differentiation?
The process of cells becoming specialised.
51
What are stem cells?
Undifferentiated cells- aren’t adapted to a particular function and have the potential to differentiate.
-able to undergo cell division repeatedly = source of new cells necessary for growth, development and tissue repair.
- once specialised they lose ability to divide, entering G0 phase.
Activity has to be strictly controlled:
- slow division = leads to ageing, tissue isn’t replaced efficiently.
- uncontrolled division= tumors (mass of cells)= cancer.
52
What is meant by potency?
A stem cell’s ability to differentiate into different cell types.
The greater the number of cell types it can differentiate into, the greater its potency.
53
What are the 3 potency levels/types?
1. Totipotent stem cells- can differentiate into any type of cell. ( eg. Fertilised egg/zygote. Eventually forms whole organism)
2. Pluripotent stem cells- can form all tissue types but not whole organisms. Present in early embryos.
3. Multipotent stem cells- can only form a range of cells within a certain type of tissue. (Eg. Haematopoetic stem cells in bone marrow)
54
Why is differentiation important?
In multicellular organisms cells have to specialise in order to take on different roles in tissues and organs.
When cells differentiate they become adapted to their particular role and this is based on the function of the tissue, organ and organ system.
All blood cells are derived from stem cells in the bone marrow.
55
Explain the replacement of red and white blood cells.
RBCs:
Mammalian erythrocytes are essential for transport of O2 around the body.
- due to lack of nucleus/organelles= life span is only 120 days so they need to be replaced constantly.
- stem cells in bone marrow produce 3 billion erythrocytes per kg of body mass a day to meet demand.
Neutrophils:
- essential role in immune system. Live for only 6 hours.
- stem cells produce 1.6 billion per kg per hour. This increases during infection.
56
What are the sources of animal stem cells?
1. Embryonic stem cells:
- present at early stage of embryo development.
- totipotent.
- after 7 days, blastocyst (mass of cells) is formed. Cells are now pluripotent. Remain in this state in fetus until birth.
2. Tissue/adult stem cells:
- present throughout life from birth. Multipotent.
- can be harvested from umbilical cords of newborns. Advantage as plentiful supply of umbilical cords and no surgery needed. Can be stored for future as they wouldn’t be rejected in a transplant for that individual.
57
What are the sources of plant stem cells?
Meristematic tissue (meristems):
- present wherever growth is occurring. Tips of roots and shoots.
- located between phloem and xylem tissues= called vascular cambium.
Cells in this region differentiate into the different cells present in the xylem/phloem as this ensures that vascular tissue grows as plant grows.
-pluripotent.
58
What are the uses of stem cells?
Potential of treating:
- heart disease- muscle tissue in heart is damaged.
- type 1 diabetes- insulin producing cells can be injected.
- Parkinson’s disease- caused by death of dopamine.
- Alzheimer’s disease- brain cells destroyed.
- macular degeneration- causes blindness in elderly.
- birth defects.
- spinal injuries.
Already used in:
- treatment of burns(can produce new skin).
- drug trials.
-development biology.
59
What are the ethical problems of using stem cells?
1. Removal of stem cells from embryos causes destruction of the embryos.
2. Religious objections- life begins at contraception so destruction of the embryo is murder.
lack of consensus as to whether embryo itself has rights and who owns the genetic material being used.
Use of plant/adult stem cells and those from umbilical cords overcome these issues to a decent extent, however, these cells are multipotent not pluripotent like embryonic stem cells.
Bio
flashcards
Decks in class (12)
# Cards
-
Chapter 2- basic components of living systems35
-
Chapter 11- Biodiversity38
-
C12- Communicable Disease28
-
Chapter 8- Transport In Animals72
-
Chapter 9- Transport In Plants52
-
Chapter 7- Exchange Surfaces+ Breathing43
-
Chapter 6 - Cell Cycle59
-
Chapter 10- Classification52
-
Chapter 4 - Enzymes33
-
3.8 - 3.11 Nucleic Acids32
-
Chapter 5 - Plasma Membrane26
-
Chapter 3 - Biological Molecules64
