1
Q
What are the main two phases in the cell cycle of eukaryotic cells?
A
1) Interphase
2) Mitotic phase
2
Q
What is interphase?
A
Growth period of the cell cycle between cell divisions. Consists of stages G1, S, G2.
3
Q
What happens during interphase?
A
- DNA is replicated and checked for errors in the nucleus.
- Protein synthesis occurs in the cytoplasm.
- Mitochondria grow and divide, increasing in number in the cytoplasm.
- Chloroplasts grow and divide in plant and algal cell cytoplasm, increasing in number.
- The normal metabolic processes of cells occur.
4
Q
What are the three stages of interphase?
A
1) G1- The first growth phase: cell grows in size, new organelles and proteins are made, organelles replicate.
2) S- synthesis phase: DNA is replicated in the nucleus.
3) G2- The second growth phase: the cell continues to increase in size, energy stores are increased and the duplicated DNA is checked for errors.
5
Q
What is the mitotic phase? What stages does it involve?
A
1) Mitosis- the nucleus divides.
2) Cytokinesis- The cytoplasm divides and two cells are produced.
6
Q
What is G0?
A
- G0 is the name given to the phase when the cell leaves the cycle, either temporarily or permanently.
- There are a number of reasons for this including :
1) Differentiation- A cell that becomes specialised to carry out a particular function is no longer able to divide. It will carry out this function indefinitely and not enter the cell cycle again.
2) The DNA of a cell may be damaged, in which case it is no longer viable. A damaged cell can no longer divide and enters a period of permanent cell arrest. The majority of normal cells only divide a limited number of times and eventually become senescent.
3) As you age, the numbers of these cells in your body increases. Growing number of senescent cells have been linked with many age related diseases, such as cancer and arthritis.
4) A few types of cells that enter G0 can be stimulated to go back into the cell cycle and start dividing again, for example lymphocytes in an immune response.
7
Q
What are checkpoints?
A
Control mechanisms of the cell cycle.
8
Q
Why do cells divide by mitosis?
A
1) Growth: In order for organisms to increase in size, they must increase the overall number of cells that they are made from.
2) Repair : Cells need to be replaced as they mostly do not survive indefinitely.
3) Asexual reproduction: In plants and some animal cells. Offspring produced by asexual reproduction are identical to their parents and each other.
9
Q
What is the G1 checkpoint?
A
This checkpoint is at the end of the G1 phase, before entry into S phase. If the cell satisfies the requirements of this checkpoint, it is triggered to begin DNA replication. If not, it enters a resting state. (G0) G1 checks for: - Cell size - Nutrients - Growth factors - DNA damage
10
Q
What is the G2 checkpoint?
A
This checkpoint is at the end of the G2 phase, before the start of the mitotic phase. In order for this checkpoint to be passed, the cell has to check for a number of factors such as: cell size, DNA replication, DNA damage
11
Q
What does the spindle assembly checkpoint check for?
A
It checks for chromosome attachment to spindle.
12
Q
What are chromatids?
A
Chromatids are two identical copies of DNA held together at a centromere.
13
Q
What are the four stages of mitosis?
A
1) Prophase
2) Metaphase
3) Anaphase
4) Telephase
14
Q
What happens during prophase?
A
1) The chromotin fibres begin to coil and condense to form chromosomes.
2) Protein microtubules form spindle-shaped structures linking the poles of the cell.
3) Centrioles start moving to the opposite poles of the cell.
4) The nuclear envelope breaks down.
15
Q
What happens during metaphase?
A
1) The chromosomes line up along the middle of the cell and become attached to the spindle by their centromere.
2) They form a plane in the centre of the cell, called the metaphase plane, and then held in position.
16
Q
What happens during anaphase?
A
1) The centromeres holding together the pairs of chromatids in each chromosome divide during anaphase.
2) The chromatids are separated and pulled to opposite poles of the cell by the shortening spindle fibres.
17
Q
What happens during telephase?
A
1) The chromatids have reached the poles and are now called chromosomes.
2) The two new sets of chromosomes assemble at each pole and the nuclear envelope reforms around them.
3) The chromosomes start to uncoil and the nucleolus is formed.
18
Q
What happens during cytokinesis in animal cells?
A
- A cleavage furrow forms around the middle of the cell.
- The cell-surface membrane is pulled inwards by the cytoskeleton until it is close enough to fuse around the middle forming two cells.
19
Q
What happens during cytokinesis in plant cells?
A
- Plant cells have cell walls so it is not possible for a cleavage furrow to be formed.
- Vesicles from Golgi apparatus begin to assemble in the same place as where the metaphase plate was formed.
- The vesicles fuse with each other and the cell surface membrane, dividing the cell into two.
- New sections of cell wall then form along the new sections of membrane.
20
Q
What is meiosis?
A
- A type of cell division that happens in the reproductive organs to produce gametes.
- The nucleus divides twice producing four haploid cells.
- Cells formed by meiosis are all genetically different because each new cell ends up with a different combination of chromosomes.
21
Q
What happens in Meiosis I?
A
1) Prophase I
2) Metaphase I
3) Anaphase I
4) Telephase I
5) Cytokinesis
22
Q
What happens during Prophase I?
A
- The chromosomes condense, getting shorter and fatter.
- The chromosomes then arrange themselves into homologous pairs and crossing-over occurs.
- Centrioles start moving to opposite ends of the cell, forming spindle fibres.
- The nuclear envelope breaks down.
23
Q
What happens during Metaphase I?
A
- The homologous pairs line up across the centre of the cell and attach to the spindle fibres by their centromeres.
24
Q
What happens during Anaphase I?
A
- The spindles contract, separating the homologues pairs- one chromosome goes to each end of the cell.
25
What happens during Telephase I?
- A nuclear envelope forms around each group of chromosomes.
26
What happens during cytokinesis?
- Division of the cytoplasm occurs
| - Two haploid daughter cells are produced.
27
What happens during Meiosis II?
- In anaphase II, the pairs of sister chromatids are separated- each new daughter cell inherits one chromatid from each chromosome.
- Four (genetically different) haploid daughter cells are produced- these are the gametes.
28
When do chromatids cross over?
In Prophase I.
- Homologous pairs of chromosomes come together and pair up.
- The chromatids twist around each other and small parts of chromatids cross over.
- The chromatids now have a different combination of alleles.
29
How does genetic variation come about?
1) Crossing over of chromatids
| 2) Independent assortment of chromosomes
30
What is independent assortment of chromosomes?
- When the homologous pairs line up in metaphase I and are separated in anaphase I, it's completely random which chromosomes from each pair ends up in which daughter cell.
- The 4 daughter cells produced by meiosis have completely different combinations of those maternal and paternal chromosomes.
- This is called independent assortment of the chromosomes.
- This 'shuffling' of chromosomes leads to genetic variation in any potential offspring.
31
What are specialised cells?
Cells that have a particular structure to serve a specific function.
32
How are erythrocytes (red blood cells) adapted to their role?
- Flattened biconcave shape: To increase their surface area to volume ratio. This is essential to their role of transporting oxygen around the body.
- No nucleus: To increase the space available for haemoglobin, the molecule that carries oxygen.
- Flexible: So that they are able to squeeze through narrow capillaries.
33
How are neutrophilis (type of white blood cell) adapted to their role?
- Characteristic multi-lobed nucleus: This makes it easier for them to squeeze through small gaps to get to the site of infections.
- Flexible shape: Allows them to engulf foreign particles or pathogens.
- Granular cytoplasm contains many lysosomes: They contain digestive enzymes used to attack pathogens and break down the engulfed particles.
34
How are sperm cells adapted to their role?
- Tail/flagellum: Capable of movement and contain many mitochondria to supply the energy needed to swim.
- Acrosome on head contains digestive enzymes: They are released to digest the protective layers around the ovum and allow the sperm to penetrate, leading to fertilisation.
35
How are palisade cells adapted to their role?
- Contain chloroplasts: To absorb large amounts of light for photosynthesis.
- Rectangular box shape: Can be closely packed to form a continuous layer.
- Thin cell walls: Increases rate of diffusion of carbon dioxide.
- Large vacuole: To maintain turgor pressure.
- Can move within cytoplasm: To absorb more light.
36
How are root hair cells adapted to their role?
- Long extensions: Increases surface area of the cell. This maximises the uptake of water and minerals from the soil.
- Thin, permeable cell wall: For entry of water and ions.
- Extra mitochondria in cytoplasm: To provide energy needed for active transport.
37
How are guard cells adapted to their role?
- Can change shape: When guard cells lose water and become less swollen they change shape and the stoma closes to prevent further water loss from the plant.
- Cell wall of a guard cell is thicker on one side: So the cell does not change shape symmetrically as its volume changes.
38
What is tissue?
A collection of differentiated cells that have a specialised function or functions in an organism.
39
What are the main four categories of tissues in animals?
1) Nervous tissue: adapted to support the transmission of electrical impulses.
2) Epithelial tissue: adapted to cover body surfaces, internal and external
3) Muscle tissue: adapted to contract
4) Connective tissue: Adapted either to hold other tissues together or as a transport medium.
40
Where can cilated epithelial be found?
- Respiratory tract
| - Fallopian tubes
41
What is cilated epithelial?
- Made up of ciliated epithelial cells.
- The cells have ‘hair-like’ structures called cilia on one surface that move in a rhythmic manner.
- Ciliated epithelium lines the trachea e.g causing mucus to be swept away from the lungs.
- Goblet cells are also present, releasing mucus to trap any unwanted particles present in the air.
- This prevents the particles, which may be bacteria, from reaching the alveoli once inside the lungs.
42
Where is squamous epithelial found?
- Air sacs of the lungs
- Lining of the lungs
- Blood vessels
- Lining of the heart
43
What is squamous epithelilal?
- Made up of specialised squamous epithelial cells.
- Forms lining of the lungs and allows rapid diffusion of oxygen into the blood.
- It is present when rapid diffusion across a surface is essential.
- Very thin (one cell thick)
44
What is cartilage tissue?
- Contains fibres of the proteins elastic and collagen.
- Collagen is a firm, flexible connective tissue composed to chondrocyte cells embedded in an extracellular matrix.
- Prevents the ends of bones from rubbing together and causing damage.
45
Where is cartilage tissue found?
- Outer ear
- Nose
- Ends of bones
- Between bones
46
What is muscle tissue?
- A tissue that needs to be able to shorten in length in order to move bones, which in turn move the different parts of the body.
- E.g Skeletal muscle fibres (which are attached to bone) contain myofibrils which contain contractile proteins.
47
Where is muscle tissue found?
- Found attached to bones
- Urinary bladder
- Uterus
- Artery walls
- Heart wall
48
What are the different types of plant tissues?
1) Epidermis tissue: adapted to cover plant surfaces
| 2) Vascular tissue: adapted for transport of water and nutrients.
49
What is the epidermis?
- Single layer of closely packed cells covering the surfaces of plants.
- It is usually covered by a waxy, waterproof cuticle to reduce the loss of water.
- Stomata formed by a pair of guard cells that can open and close are present in the epidermis.
- They allow carbon dioxide in and out, and water vapour and oxygen in and out.
50
What is the xylem?
- A type of vascular tissue responsible for the transport of water and minerals throughout plants.
- The tissue is composed of vessel elements, which are elongated dead cells.
- The wall of these cells are strengthened with a waterproof material called lignin, which provides structural support for plants.
51
What is the phloem?
- A type of vascular tissue in plants, responsible for the transport of organic nutrients, particularly sucrose, from leaves and stems where it is made by photosynthesis to all parts of the plant where it is needed.
- It is composed of columns of sieve tube cells separated by perforated walls called sieve plants.
52
What is an organ?
A collection of tissues that are adapted to perform a particular function in an organism.
53
What is an organ system?
Composed of a number of organs working together to carry out a major function in the body.
54
What are stem cells?
Undifferentiated cells with the potential to differentiate into a variety of the specialised cell types of the organism.
55
What does potency mean in terms of stem cells?
- 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.
56
What does pluripotent mean?
- A stem cell that can differentiate into any type of cell, but not form a whole organism.
- Present in early embryos
57
What does totipotent mean?
- A stem cell that can differentiate into any type of cell and form a whole organism.
- E.g a fertilised egg, zygote
58
What does multipotent mean?
- A stem cell that can only differentiate into a range of cell types within a certain type of tissue.
- E.g stem cells in bone marrow
59
What are the sources of animal stem cells?
1) Embryonic stem cells- these cells are present at a very early stage of embryo development and are totipotent.
2) Adult tissue stem cells- They are multipotent
60
What are the sources of plant stem cells?
- Stem cells are present in meristematic tissue (meristem).
- This tissue is found wherever growth is occuring in plants, e.g tips of roots and shoots
- In the root and stem, stem cells of the vascular cambium divide and differentiate to become xylem vessels and phloem sieve tubes.
61
Uses of stem cells
Used to treat diseases such as:
- Heart disease
- Type 1 diabetes
- Parkinson's disease
- Alzheimer's disease
- Birth defects
- Spinal injuries
A-Level Biology
flashcards
Decks in class (41)
# Cards
-
2 Basic components of living systems36
-
3.2 Water7
-
3.3 Carbohydrates19
-
3.5 Lipids14
-
3.6 Proteins28
-
3.7 Biochemical tests for molecules8
-
3.8 Nucleic acids19
-
3.9 DNA replication19
-
4 Enzymes31
-
5 Plasma membranes51
-
6 Cell division61
-
7 Exchange surfaces and breathing33
-
8 Transport in animals62
-
9 Transport system in plants31
-
10 Classification61
-
11 Biodiversity64
-
12 Communicable diseases98
-
12.7 Antibiotics and Other Medicines11
-
13.1-13.5 Neural Communication53
-
13.6-13.8 and 14.5 -14.637
-
13.9-13.10 Muscles31
-
14.1 Hormonal Communication28
-
14.2-14.4 Regulating Blood Glucose Concentration19
-
15.1-15.3 Thermoregulation30
-
15.4 Liver19
-
15.5 Structure & function of kidney35
-
15.6 Kidney & Osmoregulation10
-
15.7 Urine and Diagnosis10
-
15.8 Kidney Failure21
-
16 Plant responses46
-
17.3 Light-dependent reaction32
-
17.3 Light independent reaction15
-
17.4 Limiting factors affecting photosynthesis6
-
18 Respiration44
-
19 Genetics of Living Systems57
-
20 Patterns of Inheritance20
-
21 Manipulating Genomes49
-
22 Cloning18
-
22 Biotechnology31
-
23 Ecosystems50
-
24 Populations and Sustainability53
