2.6 cell division Flashcards
Definition of tissue
a collection of differentiated cells that together have a specialised function in an organism
Definition of organ
forms a distinct structural and functional unit within an organism that is made from more than one tissue
Definition of an organ system
a collection of organs with a particular function
Structure to function of a erythrocytes(red blood cell)
- flattened, bioconcave shape = increasse surface area for transporting oxygen
- no nucleus = more space for haemoglobin
- flexible = squeeze through narrow capillaries
Structure to function of neutrophils
- multi-lobed nucleus = squeeze through small gaps to access sites of infection
- granular cytoplasm = full of lysosomes for the breakdown of englufed pathogens
- essential role in the immune system
Structure to function of a spermatoza
- flagellum = provides motility to swim to the egg
- many mitochondria = provide ATP for swimming
- acrosome on the head = contains digestive enzymes to penetrate the outside of the egg during fertilisation
Structure to function of a palaside cell
- many chloroplasts = absorb light in photosynthesis
- retangular shape = continous layer for maximal light absorption
- thin cell walls = reduce diffusion distances of carbon dioxide
- large vacuole = maintain turgidity
- found in mesophyll layer of the leaf
Structure to function of root hair cells
- long extensions (root hairs) = increase the surface area for absorption of water and mineral ions from the soil
- found at the surfaces of the root within the epidermis
Structure to function of a guard cell
- found in pairs on the lower epidermis of the leaves
- stomato are the site of gaseous exchange in plants
- inner cell wall thick and rigid = when turgid it changes shape by curving causing the stomata pore to open
Structure to function of a squamous epithelium
- one cell thick = rapid diffusion (eg. alveoli)
- basement membrane holds the epithelium onto the other tissues
- ‘pavement epithelial’ flat
Structure to function of a ciliated epithelium
- cilia = move in a synchronised pattern to move materials
- often associated with glandular tissue that secrete mucus (goblet cells)
Structure to function of a connective tissue (cartilage)
- firm and flexible - made of chondrocyte cells embedded in the extra cellular matrix
- matrix consists of collagen fibres (strength) and elatin fibres (flexibility)
three forms:
1. hyaline - ends of bones/airways/nose
2. fibrous - vertebrae discs
3. elastic - outer ear
Structure to function of a muscle
- muscle fibres contain contractile proteins called myofilaments = bring about movement
three forms
1. skeletal = joined to bones
2. cardiac = makes up the wall of the heart
3. smooth = makes up the walls on the intestine, blood vessels, airways, uterus, and urinary tracts
Structure to function of epidermis
- made of single layer of closely packed cells = provide protective covering on leaves/ stems/ roots
- covered in waxy cuticle = prevent infection
- found with guard cells = gaseous exchange
Function of a vascular tissue - xylem
transport tissue that carries water and minerals from the roots to the rest of the plant
* consists of hollow columns of elongated dead cells lined end to end and reinforced with lignin
* lignification strengthens the cell wall and ensures that the xylem vessels do not collapse
What is the cell cycle triggered by
cyclins
What does the interphase consist of?
G1
S
G2
What happens in the G1 phase
- cell growth of the cell
- replication of organelles
- protein synthesis
What happens in the S phase
- DNA replication
- chromosomes unwound
What happens in the G2 phase
- DNA checked for errors
- respiration
What happens in the M phase
- formation of the spindle
- seperation of chromatids
- supercoiling of chromosomes
What happens in the cytokinesis phase
- division of the cell / cytoplasm
Definition of senescence
cell aging
Definition of apotosin
programmed cell death
What happens in the cell arrest phase
- check for faulty cells
What is classed as a faulty cell
- too small ( cell size )
- old age
- differentiation
- damaged DNA
What is a cyclin
- cell signaling molecule
- binds to an enzyme (CDK) they active it by altering the shape of the active site
What are the 4 stages of mitosis?
- prophase - prepare
- metaphase - middle
- anaphase - away
- telophase - together
What happens during prophase in mitosis
- chromosomes are condensed
- chromosomes and sister chromatid joined together by a centromere
- spindle fibres form
- nuclear envelope breaks down
- nucleolus disappears
What happens during metaphase in mitosis
- spindle fibres continue to extend from centrosomes
- chromosomes line up at the equator
- each sister chromatid is attached to a spindle at opposite poles
What happens during anaphase in mitosis
- the sister chromatids seperate at the centromere
- spindle fibres begin to shorten
- sister chromatids are pulled to opposite poles by the spindle fibres
What happens during telophase in mitosis
- chromosomes begin to decondense
- nuclear envelope begins to reform
- spindle fibres break down
- new nucleoli form within each nucleus
What is the significance of mitosis
- asexual reproduction
- repair tissues
- replacement of cells
- growth of mutlicellular organisms
What happens during prophase 1 in meiosis
- chromatids condense
- sister chromatids are arranged as a homologous pair (bivalent)
- non-sister chromatids may cross over called chisma
- spindle is formed
- nuclear envelope is broken down
What happens during metaphase 1 in meiosis
- bivalents line up along the equator of the spindle
- maternal and paternal chromosomes line up in the middle and independent assortment happens ( a proportion of maternal and paternal will end up on either side of the equator to allow for variation )
What happens during anaphase 1 in meiosis
- homologous pairs are seperated as the microtubles move the spindle to pull the whole chromosomes to opposite ends
- the centromeres don’t divide
What happens during telophase 1 in meiosis
- spindle fibres breaks down
- nuclear envelope forms around the two groups of chromosomes and nucleoli form
What happens during cytokensis in meiosis
- division of the cytoplasm
- cell organelles are distrubuted evenly
- cell surface membrane pinches off and creates a clevage burrow
- produces two haploid cells
What happens during prophase 2 in meiosis
- nuclear envelope is broken down and chromosomes condense
- a spindle forms
What happens during metaphase 2 in meiosis
- chromosomes line up along the equator
What happens during anaphase 2 in meiosis
- chromatids are pulled to opposite poles
- creates 4 groups of chromsomes that have half the amount from parent cells
What happens during telophase 2 in meiosis
- nuclear membranes form around each group of chromosomes
What is the signifcance of meiosis
Genetic variation and sexual reproduction
* crossing over (chiasmata) - non sister chromatids exchange alleles
* independent assortment - randomly allignment of homologous pairs along the equator of the spindle
* random fusion of gametes - any male gamete can fertilise any female gamete
Cytokinesis stage in a plant
- vesicle from golgi body containing lamella and cellulose cell wall chemicals move towards the cell centre
- vesicles form a cell plate
- new cell membrane and cell wall and divides the cell
Cytokinesis stage in an animal
- organelles distribute evenly around the nucleus
- centre of the cell pinches and forms a clevage furrow
- pulled inwards by the cytoskeleton
How is genetic variation achieved in meiosis
- Crossing over (chiasmata) = prophase 1
- Independent assortment of homologous chromosomes = metaphase 1
- Independent assortment of chromatids = metaphase 2
Define totipotency
can divide into any cell type found in the embryo and extra-embroyonic cells (placenta)
Define pluripotency
can divide into any cell type found in the embryo
Define multipotency
can divide into a limited range of cell types
What can cells in the bone marrow differentiate into
- erythrocytes
- monocytes
- neutrophils
- lymphocytes
Benefits of using stem cells
- treat a wide variety of diseases
- organs developed from own stem cells reduces risk of rejection
- already successfully using adult stem cells
Issues with using stem cells
- ethical issue - killing a baby?
- expensive to collect embryonic stem cells before birth
- risk of cultured stem cells getting a mutation
- cultured stem cells can become infected with a virus
- low number of cell donors
