2.6 - B - Cell Division, Cell Diversity & Cell Differentiation Flashcards
What is a zygote?
An egg immediately after fertilisation with spunk
Define cytokinesis
Where the cytoplasm divides following mitosis, resulting in 2 new daughter cells
Define interphase
A phase of the cell cycle where the cell is not diving; it is subdivided into growth and synthesis phases
Define mitosis
A type of (asexual reproduction) cellular division that produces daughter cells genetically identical to each other and to the parent cell.
Define apoptosis
Programmed cell death (suicide)
Define senescence
Where a cell can no longer divide
State the 2 parts of the eukaryotic cell cycle and they subdivide into
Interphase -G1/G0, S (synthesis), G2
Mitosis - mitosis
Explain what happens in the G0 phase
G0 - not all cells have this phase, a resting phase triggered during early G1. The cell may undergo apoptosis, senescence or differentiation.
Explain what the G1 phase is and what happens in it
The growth phase - ensures that the cell is ready to enter the S phase and begin DNA synthesis.
Carries out growth and normal functions such as respiration and biosynthesis (protein synthesis and replication of organelles)
Cells grow and increase in size.
Transcription of genes to make RNA occurs.
Organelles duplicate.
Explain what happens in the S (synthesis) phase
DNA replicates
Once the cell enters this phase, it is committed completely to the cell cycle
When all chromosomes have been duplicated, each one consists of 2 identical sister chromatids
It is rapid because exposed DNA base pairs are more susceptible to mutagenic agents, so reduces chance of mutation
What is chromatin made out of and how long is a chromatin thread?
DNA and histones
Approx 30nm - can’t be seen under a light microscope
What is a histone?
A protein/core that DNA is wrapped around, found inside the nucleus
Explain what happens in the G2 phase
Special chemicals ensure that the cell is ready for mitosis (checked) by stimulating (proof-reading) proteins that will be involved in making chromosomes condense and in formation of the spindle. If the genes aren’t copied properly, mutations will occur and may means the new cells don’t work/don’t make the correct proteins
Why is mitosis important?
Asexual reproduction ‐ single celled organisms divide to
produce 2 daughter cells that are separate organisms ‐ some multicellular organisms produce offspring from parts of
the parent e.g. potato runners
Growth ‐ multicelluar organisms grow by making new cells ‐ they
are identical so they perform the same job
Repair/replacement ‐ damaged or old cells need to be replace with
new gentically identical ones so they can do the same job
Why don’t bacteria carry out mitosis?
Have no linear chromosomes, spindles or centrioles
List the phases of mitosis
(Interphase) Prophase Metaphase Anaphase Telophase (Cytokinesis)
Explain what happens in prophase
Prepare
The chromosomes (sister chromatids) supercoil to shorten and
thicken (they are now visible as sister chromatids under a light microscope)
The nuclear envelope breaks down
The centriole divides in 2 and each daughter centriole goes to a pole of the cell
Spindle fibres (microtubules) begin to form
Explain what happens during metaphase
Meet in the middle
The chromosomes (sister chromatids) line up along the equator of the cell
The spindle fibres attach to the centromeres of the chromosomes
What is a centromere?
The point at which 2 chromatids are connected
Explain what happens in anaphase
Apart
The centromere breaks ‐ this separates the sister chromatids into chromosomes.
Each chromatid is identical to the original chromosome in the parent cell that it was copied from.
The spindle fibres shorten and pull the chromosomes apart to the poles of the cell.
Motor proteins, walking along the tubulin threads, pull each sister chromatids of a pair in opposite directions, towards opposite poles.
Because the centromere goes first, the now chromosomes assume a V shape.
(cytokinesisusuallystartsnowbutweconsideritseparatefrommitosis)
Explain what happens in telophase
2 (nuclei)
The separated chromosomes reach the poles.
New nuclear envelopes form around the 2 sets of chromosomes to form 2 new nuclei.
The super coiled chromosomes uncoil into chromatin.
Spindle fibres break down.
Explain what happens in cytokinesis in animal cells
The cytoplasm cleaves to finally produce the 2 new genetically identical daughter cells (both also identical to the parent cell).
This means the daughter cells can do all of the things the parent cell could do.
Explain what happens in cytokinesis in plant cells
An end plate forms where the equator of the spindle was, and new plasma membrane and cellulose cell-wall material are laid down on either side along this end plate.
This means the daughter cells can do all of the things the parent cell could do.
What are the differences between plant and animal cell cycles?
Animal cells:
Most cells will undergo mitosis and cytokinesis
Cytokinesis starts from the outside and goes in
Plant cells:
Only special cells called meristem cells can divide
Plant cells do not have centrioles
Cytokinesis starts with the formation of a cell plate where the equator was ‐ the new plasma membrane and new cell wall material is then laid down long the cell plate
Define differentiation
When stem cells become specialised to carry out a particular job/function
Before cell’s are differentiated they are stem cells (undifferentiated)
What are epithelial cells?
Cells that constitute lining tissue
What are erythrocytes?
Red blood cells
What are neutrophils?
A type of white blood cell that is phagocytic (can ingest microbes and small particles)
What are stem cells?
Unspecialised cells that are able to express all of its genes and divide by mitosis
Explain the steps in differentiation
Young cell Cell division Cell growth Cell specialisation Mature cell - unlikely or unable to divide again
Explain the need for cell differentiation and specialisation
Multicellular organisms are large and therefore have a small SA:V, which means their most of their cells are not in direct contact with the outside environment. Therefore they need specialised cells to allow gas exchange.
Single-called organisms do not need this.
What are the 3 different types of stem cells?
Totipotent cells - can differentiate to form all cell types in the body.
Pluripotent cells - can differentiate to form all cell types in the body except in the placenta (embryonic stem cells)
Multipotent cells - are limited in what cell types they can differentiate to form eg: adult stem cells
List the 3 ways that cells can differentiate
The shape of the cell can vary eg: root hair cells
The number of particular organelles can change eg: muscle cells - lots of mitochondria
Some of the contents of the cell can change eg: red blood cells
What happens for stem cells to differentiate into erythrocytes?
They lose their nucleus and other organelles - this creates more room for haemoglobin and makes it more flexible to fit through capillaries
They are filled with haemoglobin
The shape becomes biconcave discs
What is a tissue?
A collection of different types of similar, specialised cells which work together to perform a common function eg: xylem and phloem
What are organs?
A collection of tissues working together to perform a function eg: leaves
What are organ systems?
They are made up of a number of organs working together to perform an overall life function
What happens for stem cells to differentiate into neutrophils?
They produce a lot of lysosomes (containing enzymes to digest pathogens) - this is why they appear grainy
They keep their nucleus
What happens for stem cells to differentiate into spermatozoa?
They differentiate via meiosis to become haploid so when it fertilises an egg, the zygote is diploid.
It has lots of mitochondria to provide energy for movement of flagellum
Undulipodium - helps sperm to move towards an egg in the oviduct
Acrosome - enzymes stored so sperm can penetrate egg membranes
Shape - long and thin to ease movement
What happens for stem cells to differentiate into root hair cells?
Shape - large SA for osmosis and mineral uptake
Thin wall - for a short diffusion path
Lots of mitochondria - for the active transport of minerals
What is the purpose of lignin?
It allows adhesion, stops collapse and helps support xylem vessels. They are also waterproof.
How are xylem tubes created?
Meristem cells produce small cells which elongate and become lignified which kills the cell contents. The ends break down to become long hollow tubes.
How are phloem tubes created
Meristem tissues produce cells that elongate and line up need to end to form a long tube. The ends do not break down completely but form sieve plates between cells.
Where are companion cells found and what is their importance?
They lie next to each sieve tube. They play an important role in actively moving sucrose up and down the sieve tubes
List the 4 groups animal tissues are categorised into
Connective tissue - holds structured together and provides support eg: blood, bone and cartilage
Muscle tissue - contract to bring about movement
Nervous tissue - convert stimuli and carry electrical impulses
Epithelial tissue - layers and linings
List the differences between single-called organisms and multi-cellular organisms
SC - large SA:V, MC - small SA:V
SC - all cells exposed to environment, MC - not all cells…
SC - effective exchange surface for gas exchange
SC - all cells perform all functions
MC - specialised cells perform different functions
Why is meiosis important in a population?
Increases genetic variation
Increases the chance of survival if the environment changes
What are homologous chromosomes?
Matching chromosomes, but possibly different alleles for some of the genes
What are the 8 stages of meiosis
Prophase, metaphase, anaphase, telophase x2
What happens in the first division in meiosis (1st PMAT)?
Reduction division
Chromosome number reduces from diploid (46) to haploid (23)
Crossing over, variation
Explain what happens in prophase 1
Chromatin condenses and each chromosome supercoils
Nuclear envelope breaks down and spindle threads of tubulin protein form from the centrioles in animal cells
Chromosomes come together in homologous pairs
Crossing over occurs where non‐sister chromatids wrap around each
other and may swap sections so that alleles are shuffled
What is the chiasmata?
The point at which chromosomes cross over, swapping alleles and causing genetic variation
Explain what happens in metaphase 1
Pairs of homologous chromosomes, still in their cross over state
attatch along the equator of the spindle
Each attaches to a spindle thread by its centromere
The pairs are arranged randomly, this is independent assortment.
The members of each pair face opposite poles of the cell
The way that they line up here determines how they will segregate
independently when pulled apart in anaphase.
Explain what happens in anaphase 1
The chromosomes are pulled ,apart by motor proteins that drag them along the tubulin threads of the spindle.
The centromeres do not divide, and each chromosome consists of two
chromatids.
The crossed over areas seperate from each other, resulting in swapped
areas of chromosomes and allele shuffling.
Explain what happens in telophase 1
In most animal cells, 2 new nuclear envelopes form around each set of chromosomes, and the cell divides by cytokinesis. There is then a short interphase where the chromosomes uncoil.
Each new nucleus contains half the original number of chromosomes, but
each chromosome consists of two chromatids.
In most plant cells, the cell goes straight from anaphase 1 into prophase 2
Explain what happens in prophase 2
If the nuclear envelope has reformed it now breaks down.
Chromosomes coil and condense, each one consisting of two chromatids.
Chromatids of each chromosome are no longer identical due to crossing
over in prophase 1.
Spindles form.
Explain what happens in metaphase 2
The chromosomes attach by their centromere to the equator of the spindle.
The chromatids of each chromosome are randomly arranged.
The way they have been arranged will determine how they seporate during anaphase.
Explain what happens in anaphase 2
The centromeres divide.
The chromatids are pulled apart by motor proteins towards opposite poles.
The chromatids are randomly segregated.
Explain what happens in telophase 2
Nuclear envelopes form around each of the four haploid nuclei.
In animals, the two cells now divide to give four haploid cells.
In plants, a tetrad of four haploid cells is formed.
How does meiosis produce genetic variation?
Crossing over during prophase 1 shuffles alleles.
Independent assortment of chromosomes in anaphase 1 leads to random distribution of chromosomes.
Independent assortment of chromatids in anaphase 2 leads to further random distribution of genetic material.
Haploid gametes are produced which can undergo random fusion with gametes from another organism of the same species.
Explain the differences between mitosis and meiosis
Mit: genetically identical, Mei: genetically different
Mit: 2 diploid daughter cells, Mei: 4 haploid daughter cells
Meiosis crossing over
Mit: asexual, Mei: sexual
Mit: 2 cells produced, Mei: 4 cells produced
Mit: function - cell division, general growth and repair of body
Mei: function - produce gametes
# of divisions: Mit: 1 nuclear division and 1 cytokinesis
Mei: 2 nuclear and 2 cytoplasmic divisions
Define meiosis
Cellular reproduction in which the number of chromosomes are reduced by half through the separation of homologous chromosomes in a diploid cell
What are guard cells?
Found in leaf epidermis, cells that surround and control the stomata
What are palisade cells?
Closely-packed photosynthetic cells within leaves
How are palisade cells in leaves well adapted for photosynthesis (4)?
Long and cylindrical - pack closely together, less space for air to circulate. CO2 diffuses into the cells.
Large vacuole - chloroplasts are positioned nearer to the periphery of the cell, reducing diffusion distance.
Many chloroplasts - carry out photosynthesis
Contain cytoskeleton threads & motor proteins - to move the chloroplasts.
Explain the characteristics of epithelial tissue
Made up almost entirely of cells - they are very close to each other and form continuous sheets.
No blood vessels - they receive nutrients by diffusion from tissue fluid.
Some have smooth surfaces, but some have projections (either cilia or microvilli).
Short cell cycles to replace worn or damages tissue.
Specialised to function - protection, absorption, filtration, excretion and secretion.
What are immature cells in cartilage called?
Chondroblasrs.
What are the 3 types of cartilage? Where are they found/what do they do?
Hyaline - forms the embryonic skeleton, joins ribs to sternum found in nose trachea, and larynx (voice box).
Fibrous - occurs in discs between vertebrae in the backbone (spine) and in the knee joint.
Elastic - makes up the outer ear (pinnacle) and the epiglottis (flap that closes over larynx when you swallow)
What are the 3 types of muscle tissues? What are their functions?
Skeletal muscles - packaged by connective tissue sheets, Jones to bones by tendons. When these muscles contract, bones move.
Cardiac muscle - makes up the walls of the heart and allows the heart to beat.
Smooth muscle - occurs in the walls of intestine, blood vessels and uterus, it propels substances along these tracts.
What are meristems?
An area of unspecialised cells within a plant that can divide and differentiate into other cell types.
List 4 characteristics of meristems
Thin walls containing very little cellulose
No chloroplasts
Not a large vacuole
Can divide by mitosis or differentiate into other types of cells
List 11 organ systems, what they consist of and what they do
Digestive - oesophagus, stomach, etc - nutrition provides ATP and materials for growth and repair.
Circulatory - heart and blood vessels - transport blood.
Respiratory - airways, lungs etc. - breathing and gaseous exchange.
Urinary - kidneys, bladder, ureters - excretion and osmoregulation.
Integumentary - skin, hair, nails - waterproof, protect, temp regulation.
Musculo-skeletal - skeleton, skeletal muscles - support, movement, protection.
Immune - bone marrow, skin, blood etc. - protection against pathogens.
Nervous - brain, spinal chord, nerves - same as endocrine.
Endocrine - glands - communication, control, coordination.
Reproductive - dick, balls, fanny etc. - reproduction.
Lymph - lymph nodes and vessels - transports fluids back to circulatory, resists infections.
List and explain 4 potential uses in research and medicine
Bone-marrow transplants - treat diseases in blood.
Drug research - if they can be developed into particular human tissue types, new drugs can be tested first on these tissues, rather than animals/animal tissue.
Developmental biology - help us understand how multicellular organisms work better.
Repair of damages tissues or replacement of lost tissues - regenerative medicine. May eventually treat arthritis, vision and hearing loss etc.
Where can stem cells be obtained from?
Embryonic stem cells
Stem cells in umbilical-chord blood
Adult stem cells
Induced pluripotent stem cells
What are induced pluripotent stem cells (iPS cells)?
Stem cells developed in labs by reprogramming differentiated cells to switch on certain key genes and become undifferentiated.
