2.1.6 - Cell Division, Cell Diversity and Cellular Organisation Flashcards
What’s in interphase
G1
S
G2
G0
Cell has left cell cycle:
To differentiate
Apoptosis
Senescence
Senescence
Cells no longer divide
Checkpoints in cell cycle
At G1
At G2
Why are there checkpoints
To prevent uncontrolled division that would lead to tumours
To detect and repair damage to DNA
M phase
Checkpoint chemical triggers condensation of chromatin
Cell growth stops
4 stages of mitosis
Cytokinesis then occurs
G1
Cells grow
Transcription of genes to make RNA occurs
Synthesis of biological molecules occur e.g. protein synthesis
S phase
DNA replicates (doubles)
Each chromosome has two sister chromatids
Once the cell has entered this phase, it is committed to completing the cell cycle
Why does S phase happen very rapidly
Exposed DNA base pairs are more susceptible to mutagens so this phase happens quickly to reduce the chances of mutations
G2
Cells grow
Chemicals stimulate histones and formation of the spindle
Organelles duplicate
Prophase
Chromosomes condense Centrioles duplicate and move to opposite poles Mitotic spindle begins to form Nuclear envelope breaks down Nucleolus no longer visible
Metaphase
Chromosomes align at equator and attach by their centromeres
Two sister chromatids of each chromosome are attached to spindle fibres
Anaphase
Centromere splits
Sister chromatids separate from each other and are pulled towards opposite poles of the cell due to spindle fibres shortening (now chromosomes)
Telophase
Chromosomes decondense
Spindle disappears
Nuclear envelope reforms and a nucleolus reappears
Cytokinesis in an animal cell
An actin ring around the middle of the cell pinches inwards, creating an indentation called the cleavage furrow
Cytokinesis in a plant cell
The cell plate forms down the middle of the cell, creating a new wall that partitions it in two
Where does mitosis occur in plants
Roots
Shoots
Prophase I
Starting cell is diploid
Homologous chromosomes pair up and exchange fragments (crossing over of non-sister chromatids)
Metaphase I
Homologue pairs line up at the metaphase plate
The orientation of pairs is random
Anaphase I
Homologues separate to the opposite ends of the cell
Sister chromatids stay together
Telophase I
Newly forming cells at haploid
Each chromosome has 2 non-identical sister chromatids
Prophase II
Chromosomes condense
Spindle fibres begin to capture chromosomes
Metaphase II
Chromosomes line up individually along the equator
Anaphase II
Independent segregation of sister chromatids to opposite ends of the cell
Telophase II
New forming gametes are haploid
Each chromosome has just one chromatid
Reasons we get many genetically different gametes
Crossing over
Random orientation of homologue pairs
How does crossing over ensure genetically different gametes
The points where homologues cross over and exchange genetic material are chosen more or less at random
They will be different in each cell and humans undergo meiosis a lot
How does random orientation of homologue pairs ensure genetically different gametes
The random orientation in metaphase I allows for the production of gametes with many different assortments of homologous chromosomes
Why do we need mitosis
Growth
Repair
Asexual reproduction
Genetic variation in meiosis
Crossing over genetic material (allele reshuffling) in prophase I
Independent assortment of homologous chromosomes in metaphase I
Independent assortment of sister chromatids in metaphase II
Independent segregation of sister chromatids in anaphase II
How does sexual reproduction increase genetic variation
It involves the combining of genetic material from 2 individuals
Variation increases species chance of survival due to adaptations
Tissues
A group of specialised cells working together to perform a specific function
Organs
A group of tissues working together to perform a specific function
Animal tissues
Epithelial
Connective
Muscle
Nervous
Plant tissues
Epidermal
Vascular
Meristematic
Epithelial tissue
This tissue lines free surfaces in the body such as the skin, cavities of the digestive and respiratory system, blood vessels, heart chambers and walls of organs
Characteristics of epithelial tissue
Made up almost entirely of cells
Cells are very close to each other
No blood vessels
Squamous epithelium is made of specialised squamous
Ciliated epithelium is made up of ciliated epithelial cells
Squamous epithelium
Very flat cells
Only one cell thick
Form lining of lungs and of blood vessels
Ciliated epithelium
Cells that have cilia on the surface that move in a rhythmic manner
Lines the trachea
How do epithelium cells recive nutrients
Diffusion from tissue fluid in the underlying connective tissue
What does connective tissue consist of
A non-living extracellular matrix
What does a non-living extracellular matrix contain
Proteins e.g. collagen and elastin
Polysaccharides (hyaluronic acid, which traps water)
What does a non-living extracellular matrix do
Separates the living cells within the tissue
Strengthens it
Examples of connective tissues
Blood Bone Cartilage Tendons Skin Ligaments
Where is cartilage found
In the outer ear, nose and at the edge of and in between bones