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
What is cartilage composed of
Chondrocyte cells embedded in an extracellular matrix that secrete collagen
Muscle tissue is well …
… vascularised
What do muscle cells contain
Special organelles called myofilaments made of actin and myosin, these allow the muscle tissue to contract
Types of muscle tissue
Skeletal
Cardiac
Smooth
Skeletal muscle
Joined to bones by tendons, causing bones to move
Forms multinucleate fibres containing protein filaments that slide pass each other
Cardiac muscles
Makes up the walls of the heart, allowing it to pump
Forms cross-bridges to ensure that the muscle contracts in a squeezing action
Smooth muscle
Lines walls of intestines, blood vessels, uterus and urinary tracts
Propels substances along these tracts
What does epidermal tissue consist of
Flattened cells that apart from guard cells lack chloroplasts and form a protective covering over leaves, stems and roots
What do some epidermal cells have
Walls with a waxy substance (cuticle)
Important as reduces water loss - plants in dry areas
What does meristematic tissue contain
Stem cells
From this all other plant tissues are derived
Where is meristematic tissue found
Meristems:
At root and shoot tips
In the cambium of vascular bundles
Features of meristem cells
Have thin walls containing little cellulose
Do not have chloroplasts
Do not have a large vacuole
Divide by mitosis and differentiation into other types of cell
What is vascular tissue concerned with
Transport
Xylem vessels
Carry water and minerals from roots to all parts of the plant
Phloem sieve tubes
Transfer the products of photosynthesis in solution from leaves to parts of the plant that do not photosynthesise, such as roots, flowers and growing shoots
Contains sieve tube elements and companion cells
How do xylem derive from cambium
Differentiation
Lignin is deposited in cell wall - reinforcement and waterproofing
Kills the cells - non - living xylem cells
Ends of cells break down so xylem forms continuous columns with wide lumens to carry water and dissolved minerals
Lignification is incomplete in some areas -> bordered pits
How do phloem derive from cambium cells
Differentiation:
Sieve tubes lose most of their organelles and sieve plates develop between them from the numerous sieve pores that develop
Companion cells retain their organelles and continue metabolic functions to provide ATP for the active loading of sugars into the sieve tubes
Function of roots
Anchorage in soil
Absorption of mineral ions and water
Storage
Life processes carried out by the digestive system
Nutrition to provide ATP and materials for growth and repair
Life processes carried out by the circulatory system
Transport to and from cells
Life processes carried out by the respiratory system
Breathing and gaseous exchange excretion
Life processes carried out by the urinary system
Excretion and osmoregulation
Life processes carried out by the integumentary system
Waterproofing
Protection
Temp regulation
(Skin, hair and nails)
Life processes carried out by the musculoskeletal system
Support
Protection
Movement
Life processes carried out by the immune system
Protection against pathogens
Life processes carried out by the nervous and endocrine systems
Communication
Coordination
Control
Life processes carried out by the lymphatic system
Lymph nodes and vessels transport fluid back to the circulatory system and is also important in resisting infections
Why are stem cells able to express all their genes
All genes are switched on
Potency
A cell’s ability to differentiate
Totipotent
Can differentiate into any type of cell and produce a whole organism (zygote)
Pluripotent
Can form all tissue types but not produce an organism
Multipotent
Can become any type of cell within a group of cells e.g. any type of blood cell
Sources of stem cells in humans
Embryonic stem cells
Umbilical cord blood
Adult stem cells found in bone marrow of flat bones, skin, adipose tissue, brain, blood
iPS (induced pluripotent stem cells)
iPS
Developed in lab by reprogramming differentiated cell’s to switch on genes and become pluripotent
Current uses of stem cells
Bone marrow transplants (used to treat sickle-cell anaemia and leukaemia)
Drug research (check toxicity)
Test effectiveness of medicines
Study cell function to find out what can make it fail
Developmental research - studying cells to see how they develop into diff cell types
Types of blood cells produced from stem cells
Erythrocytes
Neutrophils
Haploid
Having only one set of chromosomes
Homologous
Matching chromosomes, containing the same genes at the same places (loci)
May contain different alleles for some of the genes
Diploid
Having two complete sets of chromosomes (found as pairs)
Maternal homologues
These chromosomes will have the same genes as the maternal homologue in the chromosome pair
Paternal homologues
These chromosomes will have the same genes as the paternal homologue in the chromosome pair
Non-sister chromatids
Replicated of chromosomes, originating from different chromosomes
How are palisade cells adapted
Long and cylindrical - able to pack several together
Chloroplasts - absorb as much light as possible
Large vacuole - stores nutrients/water, provides structural support, stores waste
Cytoskeleton / motor proteins - moves chloroplasts to reduce CO2 diffusion pathway
How are sperm cells adapted
Mitochondria - releases energy for movement
Acrosome - digestive enzymes (egg)
Protein fibres in flagellum - enable rapid movement/ strength
Nucleus - contains genetic info (haploid gamete)
How are guard cells adapted
Thicker inner wall - so cell doesn’t change symmetrically when turgid
Large vacuole - to take up water and expand stoma
Active pump - move water in/out to alter water potential of cell
Stomata - O2 and CO2 can diffuse out
How are ciliated epithelial cells adapted
Cilia - move mucus
Goblet cells - produce mucus and trap harmful substances
How are squamous epithelial cells adapted
Flat - cover a large area
Thin - short diffusion pathway
How are neutrophils adapted
Membrane bound receptors - recognise materials that needs to be destroyed
Well developed cytoskeleton - enable movement
Many mitochondria - release energy needed
Multi lobed nucleus - easy to squeeze through small gaps
Granular cytoplasm - contains lysosomes w/ digestive enzymes to attack pathogens
How are erythrocytes adapted
No nucleus - more space for haemoglobin
Small and flexible - fit through capillaries
Flattened bioconcave shape - increase SA:V - take in more O2
Well developed cytoskeleton - allows it to change shape
How are root hair cells adapted
Long extension - increase surface area for diffusion
Active pump - absorb mineral ions and water through active transport
Thin cell wall - short diffusion pathway
Vacuole containing sap - low water potential (sugars and ions) - water can diffuse in
How are sieve tube elements and companion cells linked
By numerous plasmodesmata
Plasmodesmata
Connections between cells where the cytoplasm is continuous
Homologous pair of chromosomes
Chromosomes that contain same alleles
Same length
Centromeres in same position
Bivalent
Pair of homologous chromosomes
G1 checkpoint
Checks cell is ready for S phase
G2 checkpoint
Checks DNA has replicated correctly
Do plant cells have centrioles
No
Centromere
Where each chromatid touches (usually in the middle)
Why is the second division in meiosis different to mitosis
The separating chromatids of a pair aren’t the same
Where are erythrocytes and neutrophils produced
Stem cells in bone marrow
What are spindle fibres made from
Proteins
In what stage of meiosis are chiasmata formed
Prophase I
Why is the formation of chiasmata an important feature of meiosis
It provides opportunities for new genotypes to arise
Telomere
A region of repetitive nucleotide sequences at the end of a chromatid
How are erythrocytes formed from stem cells
Haemoglobin is synthesised
Organelles associated w/ protein synthesis are digested
Examples of pluripotent cells
Embryonic cells in blastocyst
Examples of totipotent cells
Stem cells of fertilised eggs
Meiosis in plant cells
Skip from Anaphase 1 to Prophase 2
Muscle tissue
Group of cells that can contract together
