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OCR Biology AS Level > 2.6 - Cell Division, Cell Diversity and Cellular Differentiation > Flashcards

2.6 - Cell Division, Cell Diversity and Cellular Differentiation Flashcards

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1
Q

What is the eukaryotic cell cycle?

A

This is the cycle in which a cell reproduces and produces two identical DAUGHTER cells. There are two main phases; INTERPHASE and METAPHASE. goo.gl/UHEu5V

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2
Q

What are cell cycle checkpoints? Give examples and explain their importance.

A

There are two main cell cycle checkpoints that you should know about - the G1/S AND G2/M CHECKPOINT. They are used to ensure that every thing is in order before the cycle continues. They prevent uncontrolled division which would lead to tumours (cancer) forming and they detect any damage to the DNA and attempt to repair it. If this is not possible they start apoptosis (programmed cell death) upon the cell. They also prevent the cycle from reversing and make sure that DNA is only replicated once every cycle.

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3
Q

What is the G1 (gap 1) phase?

A
  • Cells GROW.
  • Transcription of the genes which makes RNA -Organelles in the cell duplicate.
  • Biosynthesis takes place in this stage e.g. protein synthesis to make the enzymes requires needed for the DNA replication.
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4
Q

What is the G0 (gap 0) phase?

A
  • A resting phase which is triggered during G1.
  • Cells may undergo apoptosis, differentiation or senescence (old age - no longer able to divide)
  • Some cells such as neurones remain in this stage for a very long time or INDEFINITELY.
  • Some cells such as the epithelial cells which line the gut don’t have this stage.
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5
Q

What is the S (Synthesis) phase?

A
  • The cell is now committed to completing the cycle.
  • EVERY MOLECULE OF DNA REPLICATES.
  • Housekeeping genes (active in all cells) are replicated first
  • Genes normally inactive in a specific type of cell are replicated last.
  • Produces identical sister chromatids
  • Cell is very quick to occur as the bases are more susceptible to mutation when exposed.
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6
Q

What is G2 (gap 2) phase?

A

This is the stage which ensures the cell is ready for mitosis. The cells grow and special chemicals stimulate the proteins which are needed in mitosis.

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7
Q

What is the M (Mitosis) Phase?

A

This is the stage where nuclear division occurs and consists of further sub-phases. After this cytokinesis occurs which is the division of the cytoplasm.

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8
Q

Why is Mitosis important? (3)

A
  • ASEXUAL REPRODUCTION - single celled organisms such as Proctoctists ( Amoeba etc.) divide by mitosis to produce new individuals,
  • GROWTH - all multicellular organisms grow by producing more genetically identical cells.
  • TISSUE REPAIR - wounds are healed when a growth factor stimulates the proliferation (reproduction) of endothelial and smooth muscle cells.
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9
Q

What is the first stage of mitosis?

A

PROPHASE - The chromosomes now shorten and thicken as DNA supercoils.

  • Nuclear envelope breaks down
  • Centriole ( found in the centrosome) divide to produce two centrioles which move to opposite poles of the cell.
  • A tubulin thread forms a spindle between the centriole
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10
Q

What is the second stage of mitosis?

A

METAPHASE - the pairs of chromosomes attach to spindle at the equator of the cell by their centromeres.

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11
Q

What are the stages of mitosis?

A

P - PROPHASE
M - METAPHASE
A - ANAPHASE
T - TELOPHASE

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12
Q

What is the third stage of mitosis?

A

ANAPHASE - The centromeres of the chromatid pairs splits. The chromatids are transported by the motor proteins towards each pole of the cell

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13
Q

What is the final stage of mitosis?

A

TELOPHASE - This is a transient stage where two nuclei are within the cell as two nuclear envelopes from around the chromosomes at each pole.

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14
Q

What is cytokinesis?

A

In a plant cell an end plate forms at the equator of where the spindle was. Plasma membrane is laid down on either side of the ENDPLATE. In an animal cell there a pinching off at the middle of the cell which produces two daughter cells.

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15
Q

What is the importance of Meiosis?

A

It is really important for sexual reproduction. This is very also important for genetic variation within a population due to random fertilisation.

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16
Q

What are the two divisions of Meiosis?

A

Meiosis is split into Meiosis 1 and Meiosis 2. Meiosis 1 is the REDUCTION stage where two haploid cells are produced. Meiosis 2 is similar to Mitosis which produces 4 haploid gametes.

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17
Q

What is Meiosis?

A

A human somatic (body) cell contains 23 pairs of homologous (same genes, not necessarily identical) chromosomes. Meiosis produces the difference in the homologous chromosomes by making a difference in the alleles.

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18
Q

How does Meiosis produce genetic variation?

A

During Prophase 1 there is the crossing over of alleles. Independent assortment of chromosomes in anaphase 1 means that there is a random distribution of genetic material.There is also random distribution of the chromatids during anaphase 2. Haploid gametes can undergo random fusion with another gamete.

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19
Q

What is the first stage of meiosis 1?

A

PROPHASE 1 - before Meiosis, during the S phase of interphase, the DNA is replicated into a pair of sister chromosomes.

  • During Prophase, the chromatin condenses and each chromosome supercoils to form two chromatids.
  • Chrimatis are arranged into homologous pairs: maternal and paternal homologues
  • Nuclear envelope breaks down
  • Crossing over of non- sister chromatids and sections of the alleles are changed.
  • Spindle threads form between the centrioles.
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20
Q

What is the second stage of Meiosis 1?

A

METAPHASE 1 is where the pair of homologous chromosomes still in their crossed over state attach along of the equator of the spindle by their centromeres.
- Homologous pair assigned randomly, one out of each pair face opposite poles. The way that the homologous pairs line up determine how they are split during anaphase. This is INDEPENDENT ASSORTMENT.

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21
Q

What is the third stage Meiosis 1?

A

ANAPHASE 1 - Members of each pair of homologous chromosomes are separated by motor proteins.

  • Centromeres do not divide and each chromosome is made up of two chromatids.
  • Crossed over areas separate from each other leading to ALLELE SHUFFLING
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22
Q

What is the final stage of Meiosis 1?

A
  • In animal cells two nuclear envelopes form around each set of chromosomes, then the cell divides by cytokinesis. Then during interphase the chromosome uncoils.
  • Each nucleus contains half number of chromosomes but two chromatids
  • Plants move straight to Prophase 2.
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23
Q

What is the first stage of Meiosis 2?

A

Prophase 2- If the nuclear envelopes have been reformed, they are now broken down. Chromosomes coil and condense, each one consisting of two chromatids.

  • These are not identical due to crossing over
  • Spindles form
24
Q

What is the second stage of Meiosis 2?

A

METAPHASE 2 - Chromosomes attach to equator of the spindle with their centromeres
- Independent assortment of chromatids

25
Q

What is the third stage of Meiosis 2?

A

ANAPHASE 2 - Centromeres divide. Chromatids are pulled apart by motor proteins.
Random segregation of chromatids

26
Q

What is the final stage of Meiosis two?

A

TELOPHASE 2 - Nuclear envelopes form around the four haploid nuclei. In animal cells it divides to give four haploid cells. In a plant a TETRAD of four haploid cells is formed

27
Q

Why is there a need for differentiation and specialisation?

A
  • In a multicellular organism there is a small SA/V ratio in comparison to single celled. Most cells are NOT in DIRECT contact with the external environment therefore each cell needs to specialised to carry out a specific function in order to sustain life.
28
Q

What is differentiation?

A

An undifferentiated cell such as an embryonic stem cell becomes differentiated as certain genes are turned off and others are expressed more.
- Proportions of different organelles changes
- Shape of cell changes
- Contents of cell changes
This makes the cell specialised for a certain function.

29
Q

How are Erythrocytes specialised animal cells?

A

Erythrocytes (Red Blood Cells) carry oxygen in the blood from the lungs to respiring cells.

  • They are SMALL (7.5 micrometres in width)
  • They have a HIGH SA/V ratio
  • BICONCAVE SHAPE
  • Well developed CYTOSKELETON for FLEXIBILITY
  • Lose most ORGANELLES - no nucleus, mitochondria etc. Increases SPACE for haemoglobin molecules
30
Q

How are Neutrophils specialised animal cells?

A

Most abundant type of white blood cells.

  • DOUBLE the size of erythrocytes
  • MULTI-LOBED (split and connected) nucleus increases FLEXIBILITY
  • Attracted by CHEMOTAXIS
  • Lysosomes in their cytoplasm contain hydrolytic digestive enzymes to break down engulfed pathogens
31
Q

How are Spermatozoa specialised?

A
  • Have many MITOCHONdRIA for aerobic respiration to move the undulipodium (tail)
  • Small, long and thin - easier for MOVEMENT
  • Have a specialised lysosome ( ACROSOME) which digests the outer covering of ovum
  • Head contains haploid male gamete, little cytoplasm
32
Q

How are Epithelial cells specialised?

A
  • Squamous cells are flattened

- They have cilia

33
Q

How are Palisade cells specialised plant cells?

A

Adapted for photosynthesis

  • LONG and CYLINDRICAL - can pack closely together
  • A little space for air to circulate and CO2 to diffuse into the cells
  • Many chloroplasts
  • Cytoskeleton threads and motor proteins to move the chloroplasts nearer to surface at low light intensity
34
Q

How are Guard cells specialised plant cells?

A
  • Guard cells are found in pairs with a gap between them forming a pore used for gas exchange (stomata).
  • Light energy is used to produce ATP. This is used to transport potassium ions from surrounding epidermal cells, which lowers the water potential.
  • Water enters the cells by osmosis
  • Cell swells and tips bulge meaning that stoma enlarges.
  • Air can enter for gaseous exchange
35
Q

How are Root Hair Cells specialised?

A

These are epidermal cells found on the outside of plant roots.

  • Hair like projecting increase surface are
  • Mineral ions are actively transported and then water follows due to a decrease in water potential
36
Q

What is a TISSUE?

A

A TISSUE is a group of similar cells which work together to perform a certain function.

37
Q

What are the 4 main types of tissues?

A
  • EPITHELIAL or lining tissue
  • CONNECTIVE TISSUES - these hold structures together i.e. CARTILAGE
  • MUSCLE TISSUE - cells which are specialised to contract and cause movement
  • NERVOUS TISSUE - speciales to conduct electrical impulses
38
Q

What is Epithelial tissue and how is it SPECIALISED to carry out its function?

A
  • A tissue which covers and LINES free surfaces in the body such as skin, cavities of the digestive and respiratory system (gut), blood vessels etc.
  • They are very close to each other and form CONTINUOUS SHEETS. Joined together by lateral contacts.
  • No blood vessels within the tissue - nutrients gained through diffusion from tissue fluid.
  • Some have projections such as cilia or microvilli
  • Short cell cycles
  • Protects, absorbs, filtrates, excretes and secretes
39
Q

What is connective tissue and how is it SPECIALISED to carry out its function?

A

Consists of a matrix which separates the living cells in the tissue and allows it withstand force. Bone, cartilage, tendons are examples of connective tissue.

40
Q

What are the types of epithelium? (2)

A

SQUAMOUS epithelium - single layer of flat cells which line areas such as the alveoli
CILIATED EPITHELIUM - layer which contains projections called cilia. I.e. used to move mucus in the trachea

41
Q

What is muscle tissue?

A

Muscle Tissue is very well vascularised by blood vessels due to the continuous need to be replenished with oxygen for aerobic respiration. They are fibres which contain organelles called myofilaments made of the proteins actin and myosin. This allows contraction.

42
Q

What are the 3 TYPES of muscle tissue and what is their function?

A

SKELETAL MUSCLE - joins bones to tendons. When they contract, they make the bones move.
CARDIAC MUSCLE - makes up the wall of the heart and is able to withstand the high pressure to allow the heart to beat and pump blood.
SMOOTH MUSCLE - found in the walls of tracts such as intestines and blood vessels and propels substances along these tracts

43
Q

What is epidermal tissue?

A

Equivalent to epithelial tissue which form a protective covering over leaves, stems and roots. Some of the cells in the tissue contain a waxy substance which form a CUTICLE. The cuticle reduces water loss.

44
Q

What is VASCULAR tissue?

A

These are concerned with transport. There are two types - XYLEM & PHLOEM.

  • XYLEM vessels carry water and minerals away from the root
  • PHLOEM sieve tubes transfer the products of photosynthesis in solution from leaves to cells which do not photosynthesise
45
Q

What is Meristematic tissue?

A

These contain stem cells. Other plant tissues are derived from Meristematic tissue.

  • Found at the root and shoot tips and in the CAMBIUM OF VASCULAR BUNDLES
  • Thin walls, little cellulose, no chloroplasts, don’t have a large vacuole.
46
Q

Why are meristems needed?

A

As a plant cell matures, it gains a large vacuole and rigid cellulose cell wall which prevents it from dividing and producing new cells. New cells are therefore sourced from meristems through mitosis.

47
Q

How are Xylem made?

A

Some cambium cells differentiate to make XYLEM.

  • Lignin is deposited in the cell wall - reinforces and makes it waterproof. Also kills the cell
  • Ends of the cell break to form continuous columns with wide lumens to carry water etc.
48
Q

How are Phloem made?

A

Some cambium cells differentiate to form PHLOEM.

  • Sieve tubes most organelles and sieve plate form between them
  • Companion cells retain organelles to contain metabolic function to provide the ATP of active loading of sugars into the sieve tubes.
49
Q

What is an organ?

A

A collection of tissue which work together to perform the same function is called an organ.

50
Q

Name a plant organ and it’s function

A

Leaf - photosynthesis
Root - anchorage, absorption of minerals, storage
Stem - support, transportation, storage
Flower - sexual reproduction

51
Q

What is an organ system?

A

A number of organs which work together to carry out an overall life function is called an ORGAN SYSTEM.

52
Q

Name an organ system in a human, the organs involved and their life processes

A

DIGESTIVE SYSTEM - oesophagus, stomach, intestines etc. - nutrition to provide ATP, material for growth + repair
CIRCULATORY SYSTEM - heart, blood vessels - transport to and from cells
RESPIRATORY SYSTEM - airways, lungs, diaphragm, intercostal muscles - breathing, gaseous exchange
URINARY SYSTEM - kidneys, ureters, bladder - excretion and osmoregulation
INTEGUMENTARY SYSTEM - skin, hair and nails - waterproofing, protection, control temperature
MUSCO- SKELETAL SYSTEM - skeleton and skeletal muscles - support, protection, movement

53
Q

What is a stem cell?

A

Undifferentiated cells which are capable of becoming any type of cell in the organism.

  • They are PLURIPOTENT.
  • Able to express all of their genes.
  • Divide by mitosis to provide more cells for growth and repair
54
Q

What are the different sources of a stem cell ?

A
  • EMBRYONIC STEM CELLS - present in an early embryo before the zygote begins to divide
  • UMBILICAL CORD stem cells
  • ADULT STEM CELLS - found in developed tissue such as blood, brain, adipose amongst differentiated tissue. Acts as a repair system
  • INDUCED PLURIPOTENT STEM CELLS (iPS) developed in labs by reprogramming differentiated stem cells to switch on key genes.
55
Q

What are the uses of stem cells?

A
  • Bone marrow transplants to treat blood diseases such as sickle cell anaemia and leukaemia and the immune system.
  • Drug research - don’t need to test on animal tissue.
  • Developmental biology - study how cells develop, extend the abilities of embryos into later life
  • Repair of damaged or lost tissues - could be used for a bioscaffold of an organ to grow specific organs for transplanting.

OCR Biology AS Level (13 decks)

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