2.6 Cell Division, Cell Diversity And Cellular Organisation Flashcards
Three phases of cell cycle
Interphase, nuclear division (mitosis), cell division (cytokinesis)
Cyclis
Triggers the movement from one phase to another in the cell cycle by chemical signals
What happens during interphase
the cell increases in mass and size and carries out its normal cellular functions (eg. synthesising proteins and replicating its DNA ready for mitosis)
3 phases in interphase
G1 phase
S phase
G2 phase
What is the cell cycle
Process all body cells use to grow and divide
What are the functions of the cell cycle
Growth, repair, replace and asexual reproduction
End products of the cell cycle
2 identical daughter cells
G1 phase
Growth phase of cells
Organelles replicate
Synthesis of proteins
S phase
Replication of each chromosome resulting in each chromosome consisting of two identical sister chromatids
G2 phase
The cells continues to grow and the new DNA that has been synthesised is checked
Mitosis phase (M phase)
Where cell divides (mitosis and cytokinesis)
4 stages of mitosis
Prophase, metaphase, anaphase and telephase
Cytokinesis
Once the nucleus has divided into two genetically identical nuclei, the whole cell divides and one nucleus moves into each cell to create two genetically identical daughter cells
Cytokinesis in animal cells
cytokinesis involves constriction of the cytoplasm between the two nuclei
Cytokinesis in plant cells
A new cell wall is formed
Checkpoints throughout the cell cycle
where the genetic information contained within the replicated DNA is checked for any possible errors
During, G1, S, G2, metaphase
How to remember stages of mitosis
PMAT
G1 checkpoint
chromosomes are checked for damage. If damage is detected then the cell does not advance into the S phase until repairs have been made
S phase checkpoint
chromosomes are checked to ensure they have been replicated. If all the chromosomes haven’t been successfully replicated then the cell cycle stops
G2 checkpoint
an additional check for DNA damage occurs after the DNA has been replicated. The cell cycle will be delayed until any necessary repairs are made
Metaphase checkpoint
the final check determines whether the chromosomes are correctly attached to the spindle fibres prior to anaphase
Prophase
Chromosomes condense and thicken
Consists of sister chromatids joined at the centromere
Two centrioles migrate to opposite poles of the cell
Spindle fibres attach to specific areas on the centromeres and start to move chromosomes to the equator of the cell
Nuclear envelope disappears
Metaphase
Individual sister chromatids are moved by the spindle fibres to align at the equator
Sister chromatids are attached to the spindle by the centromere
Anaphase
Centromeres holding the pairs of chromatids in each chromosome divide
Sister chromatids separate
Spindle contracts
Each chromatids is pulled by their centromere to opposite poles of the cell
Telophase
Chromatids reached pomposity poles. They uncoil now chromosomes
Spindle fibres disappear
Nuclear envelope reforms and enclose around the chromosomes at each pole
Where does growth in plants occur
Meristems
What can be used to study mitosis
The root tip meristem
Method to see stages of mitosis in root tip meristem
Remove tip of roots and place in a suitable stain the stained root tip is gently squashed on a glass slide using a blunt instrument
Cells undergoing mitosis can be seen and drawn
Mitosis
The process of nuclear division by which two genetically identical daughter nuclei are produced that are also genetically identical to the parent nucleus
Products of mitosis
Two genetically identical daughter cells
How to mitosis lead to growth on multicellular organisms
Genetically in detail daughter cells enable unicellular zygotes to grow into multicellular organisms
How does mitosis lead to replacement of cells and repair of tissues
Damaged tissues can be repaired by mitosis followed by cell division
As cells are constantly dying they need to be continually replaced by genetically identical cells
Asexual reproduction
the production of new individuals of a species by a single parent organism – the offspring are genetically identical to the parent
How does mitosis lead to Asexual reproduction
For unicellular organisms such as Amoeba, cell division results in the reproduction of a genetically identical offspring
For multicellular organisms, new individuals grow from the parent organism (by cell division) and then detach (‘bud off’) from the parent in different ways
Meiosis
The process by which gametes are made in reproductive organs. It involves the reduction division of a diploid gem line cell into four genetically distinct haploid nuclei
End products of meiosis
4 haploid daughter cells
Stages of meiosis
Interphase
Pmat 1
Interphase
Pmat 2
Stages of meiosis
Interphase
Pmat 1
Interphase
Pmat 2
Homologous chromosomes
Pairs of chromosomes that contain the same genetic information
Sister chromatids
Each chromosome is made up of two copies- each one in a chromatid
Two chromatids called sire chromatids are joined together at the centromere
Interphase
Stage of cell cycle where cell prepares for division
Prophase 1
Crossing over occurs here
Chromosomes condense, nuclear membrane dissolves, homologous chromosomes form bivalents, nuclear envelope dissolves
Metaphase 1
Homologous pairs chromosomes assemble along the membrane plate, spindle fibres from opposing centrosomes connect to bivalents and align them along the middle of the cell
Anaphase 1
Independent assortment occurs here
Spindle fibres contract and split the bivalent, homologous chromosomes moved to opposite poles of the cell
Telophase 1
Chromosomes decondense, nuclear membrane may reform, cell divides (cytokinesis) to form two haploid daughter cells
Prophase 11
Chromosomes condense, nuclear membrane dissolves, spindle fibres reform, centromeres move to opposite poles
Metaphase 11
Spindle fibres form opposing centromeres attach to chromosomes and align them along the cell equator
Anaphase 11
Centromere divides, pairs of sister chromatids are separated, each new daughter cell inherits one chromatid from each chromosome, Spindle fibres contract
Telophase 11
Chromatids uncoil and decondense, spindle fibres break down, nuclear envelopes reform, the cell undergoes cytokinesis
Cytokinesis
Cytoplasm and surface membrane divide, creating four independent haploid cells
Crossing over
Process by which non-sister chromatids exchange alleles
Crossing over process
- Homologous pairs of chromosomes associate / form a bivalent
- Chiasma(ta) form (the point of breakage)
- (Equal) lengths of (non-sister) chromatids / alleles are exchanged
- This produces new combinations of alleles
Independent assortment process
1) Each homologous pair of chromosomes in your cells is made up of one chromosome from your mum (maternal) and one chromosome from your dad (paternal).
2) When the homologous pairs line up in metaphase I and are separated in anaphase I, it’s completely random which chromosome from each pair ends up in which daughter cell.
3) So the four daughter cells produced by meiosis have completely different combinations of those maternal and paternal chromosomes.
4) This is called independent assortment (separation) of the chromosomes.
5) This ‘shuffling’ of chromosomes leads to genetic variation in any potential offspring.
Independent assortment
the production of different combinations of alleles in daughter cells due to the random alignment of homologous pairs along the equator of the spindle during metaphase I
Erythrocytes function
transport oxygen around the body and carbon dioxide to the lungs
Erythrocytes adaptations
They are biconcave in shape which increases the surface area over which oxygen can be absorbed
The cytoplasm contains high amounts of the pigment haemoglobin which can readily bind to oxygen
No nucleus is present which makes more space inside the cell for haemoglobin molecules for maximum oxygen-carrying capacity
Elastic membrane allows the cell to be flexible and change shape as it squeezes through narrow capillaries
Neutrophils function
destroy pathogens by phagocytosis and the secretion of enzymes
Adaptations of neutrophils
Neutrophils have a very flexible shape that allows them to squeeze through cell junctions in the capillary wall
Their flexibility also enables them to form pseudopodia (cytoplasmic projections) that engulf microorganisms
There is a large number of lysosomes present in the cell. These digestive enzymes help to digest and destroy invading cells
A flexible nuclear membrane further helps the cell to penetrate cell junctions. It is thought that this flexibility is what causes the characteristic lobed nucleus
Sperm cells function
reproduction - to fuse with an egg, initiate the development of an embryo and pass on fathers genes
Adaptation of sperm cells
The head contains a nucleus that contains half the normal number of chromosomes (haploid, no chromosome pairs)
The acrosome in the head contains digestive enzymes that can break down the outer layer of an egg cell so that the haploid nucleus can enter to fuse with the egg’s nucleus
The mid-piece is packed with mitochondria to release energy (via respiration) for the tail movement
The tail rotates, propelling the sperm cell forwards and allowing it to move towards the egg
Root hair cells function
absorption of water and mineral ions from soil
Root hair cells adaptations
Root hair to increase surface area (SA) so the rate of water uptake by osmosis is greater (can absorb more water and ions than if SA were lower)
Thinner walls than other plant cells so that water can move through easily (due to shorter diffusion distance)
Permanent vacuole contains cell sap which is more concentrated than soil water, maintaining a water potential gradient
Mitochondria for active transport of mineral ions
Ciliated epithelium function
moving substances across the surface of a tissue
Adaptations of Ciliated epithelium
Have cilia (hair-like structures), which beat in a coordinated way to shift material along the surface of the epithelium tissue
Goblet cells secrete mucus which helps to trap dust, dirt and microorganisms - preventing them from entering vital organs where they may cause infection
Function of squamous epithelium
provide a surface covering or outer layer. Found on a variety of organs and structures e.g. blood vessels and alveoli
Adaptations of squamous epithelium
Squamous epithelium consists of a single layer of flattened cells on a basement membrane
The layer of cells forms a thin cross-section which reduces the distance that substances have to move to pass through - it shortens the diffusion pathway
It is permeable, allowing for the easy diffusion of gases
Function of palisade cells
carry out photosynthesis to produce glucose and oxygen
Adaptations of palisade cells
A large number of chloroplasts (the site of photosynthesis) are present in the cytoplasm to maximise the absorption of light for photosynthesis
The tall and thin shape of the cells allows light to penetrate deeper before encountering another cell wall (cell walls absorb/reflect light) and for many cells to be densely packed together
Guard cells function
control the opening of the stomata to regulate water loss and gas exchange
Adaptation of guard cells
Inner cell walls are thicker (those facing the air outside the leaf) while the outer cell walls are thinner (those facing adjacent epidermal cells). The difference in the thickness of the cell walls allows the cell to bend when turgid
The cytoplasm has a high density of chloroplasts and mitochondria. Scientists think that these organelles may play a role in the opening of the stomata
Tissue
A group of cells that work together
Organ systems
Organs working together
Xylem vessel cells function
transport tissue for water and dissolved ions
Xylem vessel cells adaptations
No top and bottom walls between cells to form continuous hollow tubes through which water is drawn upwards towards the leaves by transpiration
Cells are essentially dead, without organelles or cytoplasm, to allow free movement of water
Outer walls are thickened with a substance called lignin, strengthening the tubes, which helps support the plant
Phloem vessel cells function
transport of dissolved sugars and amino acids
Phloem vessel cells function
transport of dissolved sugars and amino acids
Adaptations of phloem vessel cells
Made of living cells (as opposed to xylem vessels which are made of dead cells) which are supported by companion cells
Cells are joined end-to-end and contain holes in the end cell walls (sieve plates) forming tubes that allow sugars and amino acids to flow easily through (by translocation)
Cells also have very few subcellular structures to aid the flow of materials
Function of muscle cells
Contraction for movement
Adaptations of muscle cells
There are three different types of muscle in animals: skeletal, smooth and cardiac (heart)
All muscle cells have layers of protein filaments in them, these layers can slide over each other causing muscle contraction
Muscle cells have a high density of mitochondria to provide sufficient energy (via respiration) for muscle contraction
Skeletal muscle cells fuse together during development to form multinucleated cells that contract in unison
Ciliated epithelium function
moving substances across the surface of a tissue
Adaptation of Ciliated epithelium
Have cilia (hair-like structures), which beat in a coordinated way to shift material along the surface of the epithelium tissue
Goblet cells secrete mucus which helps to trap dust, dirt and microorganisms - preventing them from entering vital organs where they may cause infection
Squamous epithelium function
provide a surface covering or outer layer. Found on a variety of organs and structures e.g. blood vessels and alveoli
Squamous epithelium adaptation
Squamous epithelium consists of a single layer of flattened cells on a basement membrane
The layer of cells forms a thin cross-section which reduces the distance that substances have to move to pass through - it shortens the diffusion pathway
It is permeable, allowing for the easy diffusion of gases
Cartilage function
To provide support
Cartilage adaptations
Cartilage is a strong and flexible tissue found in various places around the body
One place is in rings along the trachea, called Tracheal rings
These rings help to support the trachea and ensure it stays open while allowing it to move and flex while we breathe
Stem cell
a cell that can divide (by mitosis) an unlimited number of times
A cell that has not yet become a specialised cell
What can a stem cell do
Can divide many times by mitosis
Each new cell has the potential to remain a stem cell or to develop into a specialised cell such as a blood cell or muscle cell
4 types of stem cells potency
Unipotent, multipotent, pluripotent, totipotent
Unipotent
Can not differentiate, but are capable of self renewal
Self renewal
The process by which stem cells divide to make more stem cells, perpetuating the stem cell throughout life
Multipotent
Can differentiate into a number of closely related cell types within a certain type of tissue
Pluripotent
Embryonic stem cells that can differentiate into any cell type found in an embryo but are not able to differentiate into extra-embryonic cells
Totipotent
Able to differentiate into any type of cell in body including int extra embryonic cells such as those in the placenta eg. Zygote
Embryonic stem cells
Are stem cells found in embryos and can develop into almost every cell type under the right conditions in a lab
Adult stem cells
Found in adult tissue (eg bone marrow) these cells can only differentiate into the same type of liver cell as the tissue they came from
How are adult stem cells used in animals
To replace damaged cells
Things about adult stem cells
Present throughout life from birth
Multipotent
Could be artificially triggered to become pluripotent
Can be harvested from umbilical cords of newborn babies
Advantages of embryonic stem cells
Can treat a wide variety of diseases
Can become any cell type because they are pluripotent
Disadvantages of embryonic stem cells
Possible harm/death of embryo
Human rights/ ethical issues (the embryo cannot give consent)
Unreliable as this is not a well-tested method
Advantages of adult stem cells
No ethical issues as adult can give consent for the stem cells to be collected
Safer, as this is a well tested method
Disadvantages of adult stem cells
Possibility of infection during extraction of stem cells
Adult stem cells can only become one type of cell as they are multipotent
Can be very painful
How do stems cells help red blood cell production
As red blood cells lack a nucleus, they cannot divide, meaning that new erythrocytes are constantly being formed from bone marrow stem cells in order to maintain the red blood cell count in the blood
This process is known as erythropoiesis
What form the transport system of plants
Xylem vessel and phloem
What are xylem and phloem formed form
Stem cells found in tissue between them (cambium)
What type of cell is the cambium
is a meristem, which is the term given to any undifferentiated tissue in a plant that has the ability to give rise to new cells
What does cambium do
the stem cells at the inner edge of the cambium differentiate into xylem cells and the stem cells at the outer edge of the cambium differentiate into phloem cells
Cambium cells that differentiate to form the xylem lose their cytoplasm, deposit lignin in their cell walls and lose their end cell walls
Cambium cells that differentiate to form the phloem lose some of their cytoplasm and organelles, and develop sieve plates (located at ends of the cells)
Why do stem cells have huge potential in the therapeutic treatment of disease
Their ability to differentiate int multiple cell types
Where do embryos for research come from
the waste (fertilised) embryos from in vitro fertilisation treatment
This means these embryos have the potential to develop into human beings
This is why many people have ethical objections to using them in research or medicine
How many times can adult stem cells divide by mitosis
Adult stem cells can divide (by mitosis) an unlimited number of times but they are only able to produce a limited range of cell types
What do adult stem cells in bone marrow produce
used to produce different types of blood cell
What do adult stem cells in brain produce
used to produce different types of neural and glial cells
Why is use of adult stem cell less controversial
Donor is able to give permission
What needs to happen to use donated adult stem cells
they need to be a close match in terms of blood type and other body antigens
There is a chance that the cells used are rejected by the patient’s immune system
Potential uses of stem cells in medicine
repair of damaged tissues, treatment of neurological conditions and research in developmental biology
