chapter 6- cell division Flashcards
what 3 phases does interphase consist of?
- G1
- S phase
- G2
what happens in the G1 phase?
- cell grows in size
-protein synthesis - cell organelles made in preparation for division
At the end of the G1 phase it checks for correct cell size, if cell has enough nutrients, DNA damage. if it fails it will enter G0 phase
reasons a cell will enter G0 phase
- cell differentiation- can no longer divide as it is specialized
-DNA damage- no longer viable, can cause mutations
-Lymphocytes- an example of a cell that can re enter the cell cycle
what happens in the S phase?
- DNA begins to replicate
- s phase begins when DNA replication starts and ends once the final chromosome has been replicated
- happens as quickly as possible due to the high risk of exposed bass being affected by harmful chemicals such as mutagens
what happens in the G2 phase?
the gap between DNA synthesis and mitosis
the cell continues to grow
there is a G2 checkpoint to ensure the DNA has been replicated without damage. If it has been damaged the cell will try to fix it or apoptosis will occur.
define mitosis
the process of dividing and replicating te genome
define cytokinesis
the physical division of the cell
what happens during mitosis?
- starts after interphase
- referred to as the M phase
-cell growth stops
what happens during cytokinesis?
- starts after the M phase
- 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.
-In animal cells, cytokinesis involves constriction of the cytoplasm between the two nuclei and in plant cells, a new cell wall is formed
what are the 4 stages of mitosis?
- prophase
- metaphase
- anaphase
- telophase
describe prophase
- Chromosomes condense and become visible under a microscope as distinct structures, each consisting of two sister chromatids joined at the centromere.
- The nuclear envelope breaks down, and the nucleolus disappears.
- Spindle fibers begin to form from the centrioles (in animal cells), which move to opposite poles of the cell. These spindle fibers extend from the centrosomes and are essential for chromosome movement.
describe metaphase
- The chromosomes align along the equatorial plane (the metaphase plate) of the cell.
- Spindle fibers attach to the centromeres of the chromosomes via the kinetochores, ensuring that the chromosomes are properly aligned for separation.
describe anaphase
- The sister chromatids are pulled apart toward opposite poles of the cell. This occurs when the spindle fibers shorten, separating the centromeres and dividing the chromatids.
- The chromatids are now considered individual chromosomes.
-This stage ensures that each daughter cell will receive an identical set of chromosomes.
describe telophase
- Chromosomes reach the poles and start to de-condense back into chromatin.
- The nuclear envelope reforms around each set of chromosomes, creating two new nuclei in the cell.
- The nucleolus reappears in each new nucleus.
how can we increase genetic diversity in gametes?
- independent assortment
- crossing over
describe the process of crossing over
- non-sister chromatids can cross over and get entangled
- these crossing over points are called the chiasmata
- the entanglement then places stress on the DNA molecules
- as a result of this a section of chromatid from one chromosomes may break and rejoin with a chromatid from another organism
- there is usually at least one or more chiasmata present in each bivalent during meiosis
describe the process of independent assortment
- the production of different combinations of alleles in daughter cells
- Homologous chromosomes (chromosome pairs, one from each parent) are separated into different gametes during meiosis.
- During metaphase I, homologous chromosomes align randomly at the metaphase plate. This random alignment leads to different combinations of maternal and paternal chromosomes being distributed to the gametes.
- As a result, the alleles for genes located on different chromosomes assort independently of each other.
- The number of possible combinations of chromosomes is calculated using the formula 2n
- independent assortment during meiosis ensures genetic diversity by randomly distributing chromosomes into gametes, which is essential for evolution and variation in sexually reproducing organisms.
what is an organ system?
a group of organs working together to perform an essential function
what is cambium?
Cambium tissue is the layer of cells in a plant that provides unspecialized cells to promote growth.
outline the ways in genetic variation is produced.
- independent assortment (in meiosis)
- crossing over (in meiosis)
- mutations
- DNA checks during replication did not recognise damage
- Random fusion of gametes during fertilization produces genetically unique offspring
-The movement of alleles between populations due to migration.
explain why meiosis needs to have twice as many stages as mitosis (3)
- to halve chromosome number/ reduce from 2N to N.
- to separate homologous pairs of chromosomes and sister chromatids
- because DNA was previously replicated
what feature of the DNA molecule is changed as a result of mutation? (1)
the sequence of bases
what are two examples of specialized plant cells?
- palisade cells
- guard cells
what is an organ system?
multiple organs working together to carry out an overall function
what is a tissue
a group of cells working together to perform a certain function
what are the boys 4 main tissue types?
- epithelial
- connective
- muscle
- nervous
describe neutrophils (a type of white blood cell)
- has a characteristic multi- lobed nucleus which allows them to squeeze through small gaps, to the site of infections
-has a granular cytoplasm which contains many lysosomes - maintains the immune system by engulfing pathogens
Describe erythrocytes (a type of red blood cell)
- flattened biconcave shape
- large SA:V
- lots of haemoglobin
- no nucleus, so more space for haemoglobin
function= carries oxygen around the body
what are 3 specialized animal cells?
- erythrocytes
- neutrophils
- sperm cell
what is turgor pressure
The force within the cell that pushes the plasma membrane against the cell wall.
describe a palisade cell
- specialized plant cell
- present in the mesophyll
- rectangular boxed shape which are stacked together.
- large vacuole which maintains turgor pressure
- contains many chloroplasts to absorb large amounts of light for photosynthesis
- chloroplasts move within the cytoplasm to areas with more light intensity
- thin cell walls= faster rate of diffusion
describe a root hair cell
- specialized plant cell
- function= absorb water and minerals
- high SA:V
- root hair = increase SA, this maximizes the uptake of water and mineral ions from the soil
- contains mitochondria for the active transport of minerals
describe a guard cell
- specialized plant cell
- function= open and close the stomata - controls the exchange of gases
- They can open and close as a result of osmosis.
- when the cell is turgid- stomata stays open
- when the cell is flaccid- stomata open and close
- allows diffusion of oxygen and carbon dioxide
name the 3 specialized plant cells
- palisade cell
- root hair cell
- guard cell
Describe squamous epithelium
- specialized animal tissue
- made up of squamous epithelium cells- known as a pavement cell.
- extremely thin= which is good for rapid diffusion
- 1 cell thick
- forms the lining of the lungs= allows rapid diffusion of O2 into the blood
Describe ciliated epithelium cells
- specialized animal tissue
- made up of of ciliated epithelium cells.
- has hair like structures called cilia that move in a rhythmic manner
- contains goblet cells, releasing mucus to trap any unwanted particles in the air
- ciliated epithelium cells line the trachea, prevent unwanted particles entering the airways.
Describe cartilage
- specialized animal tissue
- it is a firm flexible connective tissue found in the ear, nose and in-between bones
- contains fibers from the proteins elastin and collagen
- composed of chondrocyte cells embedded in the extracellular matrix
- prevents the ends of bones rubbing together and causing damage.
Describe muscle
- specialized animal tissue
- muscle need to be able to shorten in length (contract) in order to move bones that different parts of the body
- 3 types of muscle fibers= skeletal, cardiac, smooth muscle.
skeletal muscle fibers= muscles attached to bone- contract myofibrils.
what are the specialized plant tissues?
Epidermis tissue – adapted to cover plant surfaces
Vascular tissue – adapted for transport of water and nutrients
Describe the epidermis tissue in plants
- specialized plant tissue
- single layer of closely packed cells, covering the surfaces of plants
- covered by a waxy, water proof cuticle= reduces the loss of water
- stomata formed by a pair of guard cells in the epidermis.
- stomata open and close for the exchange of gases
what are the 2 types of vascular tissue in plants
- xylem
- phloem
Describe the xylem in plants
- a type of vascular tissue
- responsible for the movement of water and mineral ions throughout the plant
- tissue is made up of vessel elements= which are elongated dead cells
- walls are strengthened with lignin= provides structural support and is waterproof.
Describe the phloem in plants
- a type of vascular tissue
- responsible for the transport of nutrients, particularly sucrose (which is made in photosynthesis) around the plant
- made up of columns of sieve tube cells separated by sieve plates
where are totipotent, pluripotent and multipotent stem cells found?
- totipotent= in a blastocyst, these outer cells will form the placenta
- pluripotent= in the inner cell mass, this will form an embryo
- multipotent= in the cardiac, nervous and digestive tissue
what are sister chromatids?
A sister chromatid refers to the identical copies formed by the DNA replication of a chromosome, with both copies joined together by a common centromere.
Describe the process of crossing over in meiosis
Process:
During meiosis 1 homologous chromosomes pair up and are in very close proximity to each other
The non sister chromatids can cross over and get entangles
These crossing points are called the chiasmata
The entanglement then places stress on the DNA molecules
As a result of this a section of chromatid from one chromosome may break and rejoin with a chromatid from another organism
The swapping of alleles is important as it can result in a new combination of alleles on the two chromosomes
There is usually at least one or more chiasmata present in each bivalent during meiosis
Crossing over is more likely to occur further down the chromosome away from the centromere
Describe the process of independent assortment in meiosis
The different combinations of chromosomes in daughter cells increase genetic variation between gametes
In prophase I homologous chromosomes pair up and in metaphase I they are pulled towards the equator of the spindle
Each pair can be arranged with either chromosome on top, this is completely random
The orientation of one homologous pair is independent / unaffected by the orientation of any other pair
The homologous pairs are then separated and pulled apart to two different poles
The combination of alleles that end up in each daughter cell depends on how the homologous pairs of chromosomes were lined up
To work out the number of different possible chromosome combinations the formula 2n can be used, where n corresponds to the number of chromosomes in a haploid cell
For humans this is 223 which calculates as 8 324 608 different combinations
what is crossing over?
the process by which non- sister chromatids exchange alleles. it is random.
what is independent assortment?
the production of different combinations of alleles in daughter checks due to the random alignment of homologous pairs along the equator of the spindle during metaphase I
what is a bivalent?
a pair of homologous chromosomes
what is the difference between a bivalent and chiasmata?
a bivalent is a pair of homologous chromosomes, while chiasmata are the points where non sister chromatids exchange alleles during crossing over
why do neutrophils have a multi-lobed nucleus?
makes it easier for them to squeeze through small gaps to get to the site of infections
Describe cartilage ( a connective tissue)
Cartilage:
*It is a connective tissue found in the outer ear, nose, at the ends of, and between the bones.
*It contains fibers of the protein’s elastin and collagen
*It is a firm, flexible connective tissue composed of chondrocyte cells embedded in an extracellular matrix
*Prevents end of bones rubbing together and causing damage. E.g. many fish have whole skeletons made of cartilage not bone.
Describe muscle tissue
Muscle:
*Muscle is a tissue that needs to be able to shorten in length (contract) in order to move bones which in turn move different parts of the body
*There are three types of muscle fibres; skeletal, cardiac and smooth muscle.
*Skeletal muscle fibres – muscles which are attached to bone – contain myofibrils (which contain contractile proteins)
