2.6 Cell Division, Cell Diversity and Cellular Organisation Flashcards
Cell Division and Cellular Organisation
what is the cell cycle
- process that all body cells in multicellular organisms use to grow and divide
- sequence of ordered events which take place in a cell, resulting in cell division
- eukaryotic organisms
what are the two phases of the cell cycle
- interphase (growth and DNA replication, and normal metabolic processes of cell)
- M phase, mitotic ( mitosis and cytokinesis)
- still a CONTINUOUS process
what growth phases is interphase divided into
G1
S1
G2
how is the cell cycle regulated
-by checkpoints
- occur at key points in the cycle to make sure it is OK for the process to continue
- if not, sends cell into G0 = rest phase where cell leaves the cycle (e.g. once differentiated, cell DNA has become damaged
what does the G1 checkpoint do
- checks that the chemicals needed for DNA replication are present
- checks for any damage to DNA
… AS before entering s phase, at the end of G1 - cell size, nutrients, growth factors too
what does the G2 checkpoint do
- checks whether all the DNA has been replicated without damage
- checks cell cycle
…AS before cell can enter mitosis, at the end of G2
what does the metaphase checkpoint do
- cell checks that all the chromosomes are attached to the spindle
…AS before mitosis can continue
what is mitosis needed for
- growth of multicellular organisms
- repairing damaged tissues
- making genetically identical cells
- asexual reproduction
what type of reproduction is mitosis
- asexual reproduction
- for some plants, animals and fungi
what happens in interphase
- cell carries out normal functions (respiration)
- cell’s DNA unravels and replicates (double its genetic content)
- organelles are synthesised so increase in number
- ATP content is increased (provides energy needed for cell division)
-G1 and G2 = cell grows and new organelles and proteins are made
-S = cell replicates its DNA
what are the 4 phases of mitosis
Prophase
Metaphase
Anaphase
Telophase
what do chromosomes look like at the start of mitosis vs the end
- double stranded
- because each chromosome has made an identical copy of itself during interphase
- by the end, they end up as single-stranded chromosomes in new daughter cell
explain the technical shape of chromosomes at the beginning of mitosis
- 2 chromosomes joined in middle by centromere (dot in middle)
- each separate strand is called a chromatid (refer to both as sister chromatids)
what happens in prophase
- the chromosomes condense, getting shorter and fatter
- centrioles (tiny bundles of protein) start moving to opposite ends of the cell, forming a network of protein fibres across it called the spindle
- the nuclear envelope breaks down
- chromosomes lie free in the cytoplasm
what happens during metaphase
- the chromosomes (each with two chromatids) line up in middle of the middle of the cell
- become attached to the spindle by the centromere
- at checkpoint, cell checks that all the chromosomes are attached to the spindle
what happens during anaphase
- the centromeres divide
- separates each pair of sister chromatids
- spindle contracts, pulling chromatids to opposite ends of the cell (centromere first)
what happens in telophase
- the chromatids reach opposite poles of the spindle
- they uncoil and become long and thin again
-they’re called chromosomes again - a nuclear envelope forms around each group of chromosomes
- now are two nuclei
what happens during cytokinesis
- the cytoplasm divides
-in animal cells, the cleavage furrow forms to divide the cell membranes - usually begins in anaphase and ends in telophase
- separate process to mitosis
what do you end up with at the end of mitosis
- two daughter cells genetically identical to the original cell and to another
PAG: how would you be able to observe cells dividing in mitosis
- stain chromosomes so that you can see them under a microscope
- would be able to watch what happens to them during mitosis
- e.g. use plant root cells under a light microscope
-interphase: chromosomes spread out and not condensed - use a SQUASH microscope slide = squashed under a cover slip = easier to see the chromosomes
what happens during sexual reproduction
gametes (egg and sperm) join together at fertilisation to form a zygote
- zygote then divides and forms a new organism
where does meiosis occur
- cell division that occurs in the reproductive organs to form gametes
why can meiosis be described as a reduction reaction
- cells begin with a full number of chromosomes to start with, but the cells that are formed have half the number of normal chromosomes (called haploids)
what type of cells does meiosis form
genetically different
- because new cells end up with a different combination of chromosomes
what are the two divisions of meiosis, and which is the reduction one?
meiosis I and meiosis II
- meiosis I is the reduction one, where the cells become haploids
how many chromosomes are there in humans
46, 23 pairs
- one from mum, one from dad
what are homologous pairs
- a pair of chromosomes which are the same size and have the same genes (though could be different versions of the gene (allele - which all have the same locus, position, on a chromosome))
- one from your mum (maternal)
- one from your dad (paternal)
what happens during prophase I
- the chromosomes condense, getting fatter and shorter
- THE CHROMOSOMES ARRANGE THEMSELVES IN HOMOLOGOUS PAIRS
- CROSSING OVER OCCURS
- centrioles start to move to opposite ends of the cell, forming spindle fibres
- the nuclear envelope breaks down
what is crossing over
- occurs during prophase I, where the homologous pairs come together and pair up ( form bivalents)
- the chromatids twist around each other and bits of the chromatis swap over
- chromatids stoll contain the same gene, but have different combination of alleles
what happens during metaphase I
- the HOMOLOGOUS PAIRS line up across the centre of the cell
- attach to the spindle fibres by their centromeres
what happens during anaphase I
- the spindle contracts, SEPARATING THE HOMOLOGOUS PAIRS
- one chromosome goes to each end of the cell
what happens during telophase I
- a nuclear envelope forms around each group of chromsomes
what happens after the first phase of meiosis
- cytokinesis
- two haploid daughter cells are produced
what happens during meiosis II
- very similar to mitosis
- in anaphase II:
- the pair of sister chromatids separate
- each new daughter cell inherits one chromatid from each chromosome
what does meiosis produce
- 4
- genetically different
- haploid daughter cells
- called gametes
which are the 2 main events in meiosis which form genetically different daughter cells
- crossing over
- independent assortment of chromosomes
how does crossing over of chromatids form genetically different daughter cells
- each of the 4 daughter cells formed contain chromatids with different alleles
- increases genetic variation across offspring
- 2 will stay same, other two will have bits of eachother mixed together
where does the independent assortment of chromosomes occur
- lining up in metaphase I
- separated in anaphase I
how does independent assortment of chromosomes lead to genetic variation
- when the homologous pairs line up in MI and are separated in AI, is is completely random which chromosomes from each homologous pair ends up with which daughter cell
-so the 4 cells produced have completely different combinations of maternal and paternal chromosomes - “shuffling” of chromosomes leads to genetic variation
what are multicellular organisms made out of
- different types of cells that are specialised for their function
- ALL have some form of stem cells
what are stem cells
- unspecialised cells that can develop into different type of cells
where are stem cells found in humans
- early embryos (develop into any type of cell)
- few places in adults, e.g. bone marrow (only develop into a limited range of cells)
what is differentiation
process by which a cell becomes specialised
(stem cells divide into new cells -> become specialised)
what are adult stem cells used for
used to replace damaged cells
how do plants use stem cells
- needed to make new roots and shoots throughout their lives, as plants are always growing
- can differentiate into various types of cells, like phloem and xylem
what is meant by stem cells being able to renew themselves
- they’re able to divide to produce more undifferentiated, stem cells
what are bones, and describe structure
- living organs
- contain nerve and blood vessels
- main bones of body have marrow in the centre
what happens in the bone marrow
- adult stem cells divide and differentiate to replace worn out blood cells
-(erythrocytes and neutrophils) - always multipotent
where are stem cells found in plants
- in the meristems (parts of the plant where growth takes place)
- always pluripotent
where do xylem vessels and phloem sieve tubes get differentiated in a plant
- in the vascular cambium (meristem cells found in between x and p)
- go on to divide and differentiate
how would stem cells be used to treat diseases
- they could replace damaged tissues in a range of diseases, as can differentiate into specialised cells
- e.g. neurological disorders like Alzheimer’s and Parkinson’s
what is Alzheimer’s and how would stem cells be used to treat it
- nerve cells in the brain die in increasing numbers
- results in severe memory loss
- stem cells could be used to regrow healthy nerve cells in patients
what is Parkinson’s and how could stem cells be used to treat it
- patients suffer from tremors they can’t control
- disease causes a loss of a particular type of nerve cell in the brain
- these cells release a chemical called dopamine, which is needed to control movement
- transplanted stem cells may be used to help regenerate the dopamine-producing nerve cells
how are neutrophils adapted
- a type of white blood cell that defends the body against disease
- FLEXIBLE SHAPE allows them to engulf foreign particles and pathogens
- have MANY LYSOSOMES in the cytoplasm, which contain digestive enzymes to break down the engulfed particles
- have a MULTI-LOBED NUCLEUS, which makes it easier for them to squeeze through small gaps and get to site of infection
how are erythrocytes adapted
- red blood cell which carry oxygen in the blood
- BICONCAVE DISC SHAPE provides a large surface area for gas exchange
- NO NUCLEUS so have more room for haemoglobin (the protein that carries oxygen)
how are epithelial cells adapted
- cover the surface of organs
- joined by interlinking cell membranes and a membrane at their base
- CILIATED= in airways, have CILIA to move particles away
- SQUAMOUS= in the lungs, are VERY THIN to allow for efficient diffusion of gases
how are sperm cells adapted
- male sex cells
- have a FLAGELLUM ( tail) so they can swim to the egg
- have lots of MITOCHONDRIA, to provide the energy to swim
- have ACROSOME, containing digestive enzymes to be able to penetrate the surface of the egg
how are palisade mesophyll cells adapted
- in leaves, do most of photosynthesis
- contain MANY CHLOROPLASTS, so they can absorb a lot of sunlight
- THIN WALLS, so carbon dioxide can easily diffuse into the cell
- LARGE VACUOLE to maintain turgor pressure
how are root hair cells adapted
- absorb water and mineral ions from the soil
- have a LARGE SURFACE AREA, for absorption
- have a THIN, PERMEABLE WALL, for entry of water and ions
- cytoplasm contains EXTRA MITOCHONDRIA, to provide energy needed for active transport
how are guard cells adapted
- found in pairs, with a tiny gap in between called the STOMA , which is the TINY PORES on the surface of the leaf used for gas exchange
- in the light, guard cells TAKE UP WATER and become TURGID
- their THIN OUTER WALL and THICKENED INNER WALLS force them to bend outwards, opening the stomata
- allows the leaf to exchange gases for photosynthesis
what is a tissue
- a group of cells (plus the extracellular material excreted by them) that are specialised to work together to carry out a particular function
- contains more than one cell type
examples of animal tissues
- squamous epithelium
- ciliated epithelium
- muscle tissue
- cartilage
what is squamous epithelium
- single layer of flat cells lining a surface ((on a basement membrane))
- found in many places
- found in the alveoli lining the lungs
what is ciliated epithelium
- layer of cells covered in cilia
- found on surfaces where things need to be moved
- in the trachea, where cilia waft mucus along
- have goblet cells to trap any unwanted bacteria
what is muscle tissue
- made up of bundles of elongated cells called muscle fibres
- 3 different types of muscle tissue:
1) smooth , found in lining of stomach wall
2) cardiac, found in the heart
3) skeletal, which you move
what is cartiliage
- a type of connective tissue found in the joints
- shapes and supports the ears, nose and windpipe
- formed when cells called chondroblasts secrete an extracellular matrix ( jelly like substance containing protein fibres) which they become trapped inside
what is xylem tissue
- plant tissue which:
1) transports water around the plant
2) supports the plant - contain hollow, dead xylem vessel strands
- contain living parenchyma cells
- strengthened by lignin
what is phloem tissue
- transports sugars around the plant
- arranged in tubes
- made of sieve cells, companion cells, and some ordinary plant cells
- each sieve cell has end walls with holes in them, so that sap can move easily through
- end walls are called sieve plates
what is an organ
- a group of different tissues that work together to perform a particular function
what are examples of organs, and state what organs tissues they contain
- LUNGS:
-contain squamous epithelial tissue in alveoli,
-ciliated epithelial tissue in the bronchi, - elastic connective tissue and vascular tissue in the blood vessels
-LEAVES:
- contains palisade tissue for photosynthesis,
- epidermal tissue to prevent water loss from leaf
- xylem and phloem tissues in the veins
what is an organ system
- a group of different organs working together to perform a particular function
what is the respiratory system and what is it made out of
- involved in breathing
- lungs
- trachea
- larynx
- mouth
- diaphragm
what is the circulatory system and what is it made out of
- involved in blood supply
- heart
- arteries
- veins
- capillaries
what is meant by the potency of stem cells
a stem cells ability to differentiate into different types of cells
- greater the potency, the more types of cells a stem cell can differentiate into
what are the 3 levels of potency
- TOTIPOTENT: stem cells that can differentiate into any type of cell, e.g. first few cells in zygote
- PLURIPOTENT: stem cells that can form all tissue types, not whole organisms, e.g. in early embryos
- MULTIPOTENT: can only form a range of cells within a tissue type, e.g. in bone marrow
