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Biology > B6 - cell division > Flashcards

B6 - cell division Flashcards

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1
Q

What are the two phases of the cell cycle?

A
  • Interphase
  • Mitotic phase
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2
Q

What are the stages of interphase?

A

G1:
- cell increases in size
- organelles synthesised
- proteins produced
- organelles replicate

S:
- DNA replication

G2:
- growth continues & produce proteins, energy stores increase & duplicated DNA checked for errors.

G0:
- STOPS, cell leaves cycle & doesn’t divide
- more cells leave the body as we age = senescent cells
- few cells that enter G0 can be stimulated to go back into cell cycle & start dividing again e.g. lymphocytes in an immune response.

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3
Q

What cells enter G0? (2)

A

Already differentiated: specialised for function, so no longer able to divide

Cells w/ damaged DNA: not viable/needed

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4
Q

What is the purpose of checkpoints in interphase?

A
  • Ensures errors don’t occur e.g. an error in DNA replication could lead to a mutation
  • monitor completion of phases before progresses to next phase, if errror, cell enters G0.
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5
Q

What are the different checkpoints in interphase and what do they check? (6)

A

G1 cp (cell begins DNA replication if it meets the requirements):
- cell size
-nutrients
- growth factors
- DNA damage

G2 cp (before start of the mitotic phase):
- cell size
- DNA replication
- DNA damage

metaphase cp (mitosis can’t proceed until this cp has passed):
- chromosomes & spindles attached & aligned

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6
Q

What is the purpose of interphase?

A
  • Period of growth, preparing cell to divide
  • cell still functions as normal
  • cells mostly in interphase, otherwise would continuously divide
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7
Q

What are the 2 types of ways in which DNA can be stored? Explain their purpose.

A

Heterochromatin:
- Tightly wound & condensed DNA
- state of chromosomes in CELL DIVISION
- genes not transcribed

Euchromatin:
- loosely wound DNA
- state of chromosomes in INTERPHASE
- easily separated & genes can be transcribed.

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8
Q

What is chromatin?

A

DNA double helix wrapped around histones(proteins)

DNA + histones = chromatin

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9
Q

What are the 2 main stages of the mitotic phase?

A
  • mitosis (nuclear division)
  • cytokinesis ( cell membrane division)
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10
Q

What is mitosis and what is it used for?

A
  • Parent cell divides into 2 genetically indentical daughter cells
  • Exact same DNA copy & num of chromosomes

used for:
- replacement/repair of tissues
- asexual reproduction
- growth

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11
Q

Explain the stages of mitosis. (5)

A

PROPHASE:
- chromosomes condense, takes up stain & becomes visible under LM
- nucleolus disappears & nuclear membrane breaks down
- spindle fibres form & centrioles move to opposite poles of cell
- spindle fibres attach to centromeres & move chromosomes to centre
- nuclear envelope completely disappears

METAPHASE:
- Spindle fibres move chromosomes & align along metaphase plate in cell’s centre
- metaphase plate equator

ANAPHASE:
- centromeres divide
- spindle fibres shorten, pulling chromatid to opposite poles of cell (v shape)

TELOPHASE:
- chromatids reach pole of cell & become chromosomes
- nuclear envelope reforms around them
- chromosomes uncoil & nucleus reforms
- cleavage furrow: (cell-surface membrane pulled in by cytoskeleton)

CYTOKINESIS:
- contractile rings of microfilaments causes constriction, membrane divides into two cells.

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12
Q

What happens to the number of chromosomes before and after DNA replication?

A
  • DNA replicated in interphase before mitosis
  • 46 single chromosomes in somatic cell before replication
  • 23 pairs of homologous chromosomes (1 maternal, 1 paternal) in body cell
  • Replicated in S phase, replicate = sister chromatid
  • 2 chromatids joined at centromere = 1 chromosome
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13
Q

What types of cells undergo mitosis and meiosis?

A

mitosis: somatic(body) cells
meiosis: cells in reproductive organs (testes & ovaries)

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14
Q

Why don’t plant cells have a cleavage furrow? And how do plant cells divide?

A
  • Have cell wall
  • cleavage furrow not possible/ NO CYTOKINESIS
  • vesicles assemble at metaphase plate & fuse together, new cell wall synthesised from vesicles
  • cell splits into 2.
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15
Q

What happens during sexual reproduction?

A
  • 2 gametes (1 from each parent) fuse & produce a zygote (fertilised egg - origin of all cells in an organism)
  • Contains 1/2 diploid num otherwise chromosomes would double after every round of reproduction.
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16
Q

What is the purpose of meiosis?

A
  • occurs in diploid cells in the reproductive organs & forms haploid gametes for sexual reproduction.
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17
Q

Describe the process of meiosis I. (5)

A

PROPHASE I:
- same as mitosis BUT homologous chromosomes pair up & form bivalents.
- Crossing over occurs (chromatids entangle)

METAPHASE I:
- same as mitosis BUT homologous pairs assemble along metaphase plate
- Independent assortment (diff/random orientation of homologous pairs means that maternal or paternal could face diff poles of cell) = more genetic variation when cell divides

ANAPHASE I:
- Homologous chromosomes split & pulled to opposite poles of cell
- chromatids stay joined together
- sections of sis chromatids (entangled from crossing over) break and rejoin at the chiasmata = exchange DNA = form recombinant chromatids
- Sis chromatids no longer identical as different allele combination.

TELOPHASE:
- same is mitosis I

CYTOKINESIS:
Diploid cell becomes haploid

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18
Q

Describe the process of meiosis II.

A

PROPHASE II:
- chromosomes condense, nuclear envelope breaks, spindle fibres form

METAPHASE II:
- individual chromosomes line along metaphase plate
- Independent assortment of chromatids not identical due to crossing over = even more genetic variation

ANAPHASE II:
-same as mitosis (chromosomes pulled)

TELOPHASE II:
- Chromosomes uncoil and form chromatin
- Nuclear envelope reforms
- nucleolus visible

CYTOKINESIS:
- 4 non-identical daughter cells.
- haploid due to reduction division.

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19
Q

In which 3 ways does genetic variation occur?

A

1) Independent assortment of homologous chromosomes in metaphase I
2) Crossing over
3) Independent assortment of chromatids in metaphase II

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20
Q

How does crossing over occur?

A

SYNAPSIS = homologous chromosomes join to form bivalents

-chromatids break & recombine

  • 4 diff chromatids
  • diff order of genes = introduces genetic variation
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21
Q

What are the properties of squamous epithelium?

A
  • 1 cell thick, flat, v smoot= rapid diffusion of O2 into blood
  • lining of blood vessels, alveoli, atria, ventricles
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22
Q

What are the properties of ciliated epithelium?

A
  • hair-like cilia
  • lines trachea & sweeps mucous away from lungs
  • goblet cells release mucous to trap unwanted particles in the air & prevent bacteria etc. reaching alveoli in lungs.
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23
Q

What are the three muscle tissues in animals?

A

Skeletal: attached to bone (have microfibrils w/ contractile proteins)

Cardiac: Heart

Smooth: wall of small intestine & arterioles etc.
-contract slowly and powerfully for long periods e.g. peristalsis.

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24
Q

What is cartilage? (3)

A
  • Specialised tissue
  • connective tissue between bones
  • contain elastin & collagen fibres
  • made of chondrocyte cells embedded in extracellular matrix
  • prevent bones rubbing against each other.
25
Q

What cells make up cartilage?

A

chondrocyte cells

26
Q

Name some connective tissues in animals.

A
  • loose (e.g. adipose)
  • dense (e.g. tendons, ligaments)
  • cartilage
  • bone
  • blood
  • lymph (transport medium)
27
Q

What is the general role of epithelial cells?

A

cover surface & form lining (1 cell thick & rest on collagen proteins)

28
Q

What is the role of the cardiovascular system? Name some organs in this organ system. (2)

A
  • Pump blood around body & provide transport system

Organs:
heart, lungs, blood vessels

29
Q

What is the role of the digestive system? Name some organs in this organ system. (4)

A
  • Breaks down large insoluble molecules into smaller, soluble ones to be absorbed into blood
  • Retains water needed by body & removes undigested material
    -Bile emulsifies fat & neutralises acid going to the small intestine

Organs:
oesophagus, stomach, small intestine, large intestine, bladder, pancreas

30
Q

What is the role of the gaseous exchange system? Name some organs in this organ system.

A
  • Extract O2 for respiration & expel CO2 from body.

Organs:
lungs, larynx, trachea, alveoli

31
Q

Sperm cells are specialised animal cells. How are they specialised for their role?

A
  • male gametes that deliver genetic info to the female gamete (egg)
  • acrosome has digestive enzymes which digest protective ovum layer, so can penetrate
  • flagellum for movement & mitochondria provides energy to swim.
32
Q

Sperm cells are specialised animal cells. How are they specialised for their role? (3)

A
  • male gametes that deliver genetic info to the female gamete (egg)
  • acrosome has digestive enzymes which digest protective ovum layer, so can penetrate
  • flagellum for movement & mitochondria provides energy to swim.
33
Q

How are erythrocytes specialised for their role? (3)

A
  • biconcave/flattened shape increases SA:V to transport O2 around body
  • No nucleus = more space for haemoglobin to carry O2.
  • flexible so can squeeze through capillaries.
34
Q

How are neutrophils specialised for their role? (2)

A
  • multi-lobed nucleus = fit through small gaps to get to infection sites.
  • Granular cytoplasm w/ many lysosomes containing enzymes to digest pathogens
35
Q

Define a tissue

A
  • group of specialised cells
  • each tissue adapted to a particular function
36
Q

Define an organ

A

collection of tissues adapted to perform a particular function in an organism e.g. leaf = organism adapted for photosynthesis

37
Q

Define an organ system

A
  • organs working together to carry out major functions in the body
38
Q

What specialised tissue covers a plant’s surface?

A

epidermis
- single layer of closely packed cells
- covered by waxy cuticle(waterproof to reduce water loss)

39
Q

What are the two vascular systems in plants adapted for transport? Briefly explain then in detail. (4)

A

Xylem:
- transport water & minerals from roots to leaves
- walls strengthened w/ lignin (waterproof structural support)
- DEAD cells

Phloem:
- transport organic nutrients & sugars from leaves & stems (made by photosynthesis) to anywhere needed
- companion cells provide energy for sieve plates, which have pores in the end walls
- Have cytoplasm but no nucleus or ribosomes (more room to transport substances)

40
Q

How are palisade cells (present in mesophyll) specialised for their function?

A
  • large vacuole to maintain turgor pressure, otherwise would fold = hard for chloroplasts to absorb light for photosynthesis.
  • Cells packed into box shape to form a continuous layer
  • Thin cell wall = more diffusion of CO2
  • chloroplasts move in cytoplasm = absorb more.
41
Q

How are guard cells specialised for their function?

A
  • thicker inner cellulose cell wall is less flexible, so guard cells bend around creating an opening
  • CO2 can enter plants for photosynthesis
  • lose water = change shape & stomata closes to prevent further water loss.
42
Q

How do guard cells create an opening in the stomata?

A
  • Actively pump K+ into vacuole
  • lowers water potential
  • water enters by osmosis
  • guard cells swell with water
  • thicker cell wall causes guard cells to curve open, creating a gap in the stomata
43
Q

How are root hair cells specialised for their function?

A
  • In root surfaces or tips
  • Long root hair extensions increases surface area to maximise uptake of water & minerals from the soil
44
Q

Magnesium and nitrates are taken up into root hair cells. What are they for?

A

magnesium: make chlorophyll
nitrates: make amino acids

45
Q

What are the different 3 types of stem cells? (in detail) (6)

A

Totipotent:
- Can differentiate into any type of cell, including extraembryonic cells such an the umbilical cord & placenta.
- Only totipotent for up to 8-cell stage

Pluripotent:
- Can form all tissues except extraembryonic tissues (placenta & umbilical cord)
- can’t form whole organism
- found in inner cell mass of blastocyst

Multipotent:
- Form a range of cells within certain types of tissue.
- No toti or pluri potent cells in a fully formed mammal, which is why we can’t regenerate body parts.
- Adult stem cells in specific tissues = multipotent
- e.g. haematopoietic stem cell in bone marrow differentiates into various types of blood cells.

46
Q

What are stem cells?

A
  • undifferentiated cells originated from mitosis or meiosis.
  • not adapted to a particular function BUT have potential to form any specialised cell = totipotent.
    e.g. a zygote divides into a whole organism as the embryo grows.
47
Q

How can one stem cell form multiple specialised cells?

A
  • Can self-renew & undergo division/mitosis indefinitely to differentiate into many different cells.
48
Q

What are the two types of self-renewal in stem cells?

A

symmetric: divides into 2 stem cells
asymmetric: divides into 1 stem cell & 1 non-stem cell

49
Q

What does differentiation mean?

A
  • cell becoming specialised for a specific function
  • must be adapted to role e.g. unique shape & specific organelles.
50
Q

What is the plant source of stem cells/human totipotent cells equivalent?

A
  • found in actively growing areas in plants called MERISTEM

MERISTEM in tips of roots & shoots & in cambium (between xylem & phloem)

51
Q

What are the sources of stem cells in animals?

A

Embryonic stem cells:
- early stages of embryo development
- totipotent

Adult stem cells:
- found in tissues such as bone marrow
multipotent
- also found in umbilical cord = plentiful supply
- can be stored

52
Q

What is a blastocyst?

A
  • Cluster of dividing cells
  • inner cell mass of a blastocyst has pluripotent stem cells
  • trophoblast sticks to wall of uterus, forming the placenta & umbilical cord.
53
Q

Name 3 ways in which stem cells can be used. (3)

A

Treating burns:
- stem cells grow on biodegradable meshes
- can produce new skin (quicker than removing from another body part)

Drug trials:
- tested on stem cells before humans & animals

Transplants:
- potential to treat diseases e.g. heart disease, alzheimers (dementia = brain cells destroyed), parkinson’s (brain)

54
Q

What are the ethical concerns surrounding stem cells from embryos?

A
  • removing stem cells from embryos often destroys them
  • destroying a potential life = murder?
  • This controversy holds back progress of treating diseases.
55
Q

What are iPSCs? And why are they so important? (4)

A

Induced pluripotent stem cells
- modify adult stem cells to act as pluripotent stem cells

Why?
- many unsuccessful organ transplants due to rejection
- turn adult stem cell into iPSC & into a specific new organ.
- eliminates rejection concern & removes ethical objections of IVF embryos as doesn’t involve the loss of an embryo.

56
Q

How can umbilical cord stem cells be used in medicine?

A
  • haematopoietic cells in blood from umbilical cord
  • differentiate into blood cells, bone, cartilage
  • used in regenerative medicine, later in the same person’s life
  • own cells = less rejection risk
57
Q

How can adult stem cells be used in medicine? (3)

A

Bone marrow transplants (haematopoietic stem cells found in bone marrow)
1) Healthy bone marrow from donor stored in freezer
2) recipient treated with high-dose chemotherapy to destroy their own bone marrow.
3) frozen healthy bone marrow transfused into recipient to replace destroyed bone marrow & produce blood cell types normally.

58
Q

Where are haematopoietic stem cells and where are they found?

A
  • Adult stem cells found in bone marrow
  • multipotent
  • differentiate into blood cell types

Biology (20 decks)

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