Chapter 6 Flashcards
What is the cell cycle
Ordered sequence of events
That takes place in a cell
Resulting in division
And formation of two identical daughter cells
What occurs during interphase
Cell grows
Organelles and proteins are made
DNA is replicated and checked for errors
Mitochondria and chloroplasts grow and divide in the cytoplasm
Metabolic processes of cells occur
G1
Proteins from which organelles are made from are produced
Organelles and replicates
S
DNA is replicated
G2
Energy stores are increased
DNA replication errors checked
Proteins made for cell division
Cell division involves 2 stages
Mitosis - nuclear division
Cytokinesis - cytoplasmic division
What is Go
Phase when the cell leaves the cycle permanently or temporarily
Why would the cell need to leave the cell cycle
Differentiation
- a cell becomes specialised to carry out a particular function indefinitely, it won’t need to divide
DNA
- dna may be damaged
Cells become senescent and are only able to divide a limited number of times
What is the point of checkpoints
They are the control mechanisms of the cell cycle
Moniteur and verify whether each stage has been accurately completed before progressing
What do checkpoints mainly check for
Cell only divides when it as grown to the right size
DNA damage
DNA replication error free
Chromosomes are attached to spindle fibres and aligned
Why is mitosis needed
For growth
Repairing damaged tissues
Asexual production
What does mitosis produce
Two genetically identical daughter cells
Interphase mitosis
Each chromosome is converted into two identical dna molecules called chromotids that are joined at the centromere - which keep the chromotids together during mitosis to make sure one of each is in the new daughter cells
Mitosis in root tips of plants
Treated with a chemical to allow the cells to be separated
Squash slides to form single layer of cells
Stained
Prophase mitosis
- Chomotin fibres coil and condensé to form chromosomes that will take up stain and become visible
- protein microtubules (centrioles) move to opposite ends of pole, form a network of protein fibres called spindle
- the fibres forming the spindle allow movement of chromosomes
- spindle fibres attach to centromere
- nuclear envelope breaks down
Metaphase mitosis
- chromosomes are moved by the spindle fibres to form a plane in the centre of the cell
- called the metaphase plate
Anaphase mitosis
- centromeres divide
- chromatids are separated and pulled to opposite sides due to shortening spindle fibres
Telophase mitosis
- chromatids reach poles
- they uncoil and become long and thin ( chromosomes)
- nuclear envelope forms around each set of chromosomes
Cytokinesis mitosis
Animal cells
Cleavage furrow forms around the middle of the cell
Cell surface membrane is pulled inwards by the cytoskeleton until it fuses around the middle
Forming 2 cells
Cytokinesis mitosis
Plant cells
Vesicles from Golgi apparatus assemble on the metaphase plate and fuse together and with the cell surface membrane
Dividing the cell in two
New plant cell wall is formed
Otherwise osmotic lysis
What is the purpose of meiosis
Happens in the reproductive organs to produce gametes
Genetically different
Haploid
Reduction division
What are homologous chromosomes
Matching pairs of chromosomes, one chromosome in the 23 pairs is a maternal chromosome and the other is paternal.
Contain the same genes at the same loci, but with a variation of those genes called alleles
Meiosis 1
Reduction division
Homologous chromosomes are separated into 2 cells
Each intermediate cell will contain a full set of genes instead of 2 = haploid
Meiosis 2
Pairs of chromatids in daughter cell are separated
4 haploid daughter cells
Prophase 1 meiosis
Chromosomes condense
Nuclear envelope disappears
Spindle formation begins
- Homologous chromosomes pair up forming bivalents
- Chromatids entangle, called crossing over
Metaphase 1 meiosis
Homologous pairs assemble on the metaphase plate
Attach to the spindle fibres via their centromeres
Independent assortment
In meiosis
Metaphase 1
Homologous pairs line up randomly along the metaphase plate
Maternal or paternal chromosomes can face either pole
Is a random process
Results in many different combinations of alleles facing the poles which results in genetic varaitaion
Anaphase 1 meiosis
Homologous chromosomes are pulled to opposite poles, chromatids stay joined
Sections of dna on chromatids that had become entangled during crossing over, break off and rejoin, resulting in a exchange of DNA
What is chiasmata
The points which the chromatids break and rejoin
What are recombinant chromatids
Anaphase 1 meiosis
Sister chromosomes that are now genetically different and no longer copies
Creates genetic variation
Caused by genes being exchanged
Telophase 1 meiosis
Nuclear membrane reforms
Chromosomes uncoil
Cytokinesis is the same as mitosis
Prophase 2 meiosis
Chromatids condense and become visible
Envelope breaks down
Spindle fibres form
Metaphase 2 meiosis
Chromatids align along the metaphase plate
This process is random and called independent assortment
Creates genetic variation
Anaphase 2 meiosis
Centromere divides and separates the chromatids
Pulling the chromatids to opposite sides of the poles, along the spindle fibres
Telophase 2 meiosis
Chromosomes uncoil to from chromatin
Nuclear envelope and nucleolus reforms
Cytokinesis is same
What are specialised cells
Cells with a specific structure to serve a specific function
Erythrocytes
Red blood cells
Flattened biconcave shape - sa:v - transport oxygen
Don’t have nuclei - more haemoglobin can be carried
Loads of haemoglobin - can bind to and transport more oxygen
Flexible - squeeze through capillaries
2
7.5
Neutrophils
White blood cells
Granular cytoplasm - has lots of lymphocytes ready to attack pathogens
Characteristic multi lobed nucleus - easier to squeeze through gaps to get to infections
Flexible - can engulf foreign particles
Many lysosomes in cytoplasm - digestive proteins
10-14
Sperm cells
Flagellum - aids their swimming
Many mitochondria - provides energy to swim
Acrosome has digestive enzymes - digest protective layers around ovum allow sperm to fertilise
Palisade cells
Contains chloroplasts - absorb large amount of light for photosynthesis , can move in cytoplasm
Box shaped cells - can pack together closely to form continuous layers
Thin cell walls - increases diffusion if co2
Large vacuole - maintain turgor pressure
Root hair cells
Long root hairs - increase sa:v
Maximises up take of water and minerals from soil
Thin cellulose wall
Guard cells
If loses water it closes - from osmotic forces
Thin outer walls and thicker inner walls - so cell does not change shape symmetrically as volume changes, ensures it opens and closes
Tiny pores for gas exchange
What are the 4 main categories of tissues in animals
Nervous - support transmission of electrical impulses Elipethial - cover body surfaces Muscle tissue - adapted to contract Connective tissue - hold tissues together, a transport medium
Squamous épithélium tissue
Flat cells
Only 1 cell thick
Good for rapid diffusion across a surface - lines the lungs
Also allows rapid diffusion of oxygen into blood
Ciliated epithelium
Hair like structures
Rhythmic manner
Sweeps mucus (produced by goblet cells) away from lungs Avoids harmful bacteria reaching lungs
Cartilage
Connective tissue
Fibres of proteins elastin and collagen
Firm and flexible
Formed when Chondroblasts secrete an extracellular matrix that traps proteins fibres
Prevents bones from rubbing together and being damaged
Muscle
Made of muscle fibres
Contain microfibrils and contractile proteins
They contract and shorten in length to move bones and body parts
What are different tissues in plants
Epidermis tissue
- adapted to cover plant surfaces
Vascular tissue
- adapted for transport of water and minerals
Plant epidermis tissue
Single layer of closely packed cells
Covered by waxy cuticle - waterproof - reduces loss of water
Contain stomata - gas exchange
Xylem tissue
Water and nutrients
Vessel - elongated dead cells
Cell walls are made of strong waterproof lignin - structural support
Phloem tissue
Transport organic nutrients
Columns of sieve tube cells
Separated by sieve plates
What is an organ
Collection of tissue adapted to perform a particular function in an organism
What does the Digestive system do = organ system
Breaks down large insoluble molecules
Absorbs nutrients into blood stream
Retains water needed by the body
Removes undigested material
What are undifferentiated cells
Cells that aren’t adapted to any particular function
Have the potential to differentiate into any specialised cells
Why can Stem cells undergo cell division over and over
Because they are the source of new cells necessary for growth development and tissue repair
Potency definition
A stem cells ability to differentiate into different cells
Totipotent
Differentiate into any type
Fertilised egg
Zygote
8/16 cells from first few mitotic divisions
Pluripotent
Can form all tissue types but not full organs
Early embryos
Multipotent
Can only form a range of cells within a certain type of tissue
Haematopoetic stem cells in bone marrow - can form into different blood cells
Embryonic stem cells
Totipotent until after 7 days when a mass of cells called blastocyst have formed
Pluripotent state until born
Tissue
Adult stem cells
Multitotent
Bone marrow
where are Stem cells located in plants
Present in meristematic tissue - meristems
Stem
Root tips
Vascular cambium
Differentiate into cells in xylem and phloem tissues - vascular tissue grows as plant grows
Ethics of stem cells
Umbilical stem cells are better than adult because they divide better and are less likely to have mutations
They are are both multipotent - less useful
What is tissue
Collection of differentiated cells that are specialised to work together to carry out a particular function
What is an organ system
A number of organs working together to carry out a major function in the body
State 3 features of a stem cell
Unspecialised
Can differentiate into any cells
Are self renewing
Difference between anaphase 1 and 11
1 = separates homologous chromosomes into sister chromatids 11 = separates sister chromatids into single chromosomes ( chromatid)
How does meiosis create genetic variation
The crossing over of homologous chromosomes in meiosis 1
- sister chromatids join and break at chiasmata, exchanging DNA
- causes chromatids in the 4 daughter cells to contain a different combination of alleles
Independent assortment in meiosis
- line up randomly
- causes daughter cells to contain any combination of maternal or paternal chromosomes
Mutation
- changes the nucleotide base sequences - different protein formed
Random fertilisation - produces a large number of allele combinations
Stem cells definition
Undifferentiated cells with the potential to differentiate into any specialised cell types
Functions of stem cells
Become tissue and organ specific cells
Repair and replace damaged cells
Growth
Renew themselves
How do stem cells renew themselves and what happens when they differentiate
Renew themselves by dividing to produce more undifferentiated cells
Once they are specialised they can’t divide and enter Go phase
specialised definition
Having a particular structure to carry out a specific function
Where does the production of erythrocytes and neutrophils take place
Adult stem cells divide and differentiate to make blood cells
In bone marrow
Where does the production of xylem vessels and phloem sieve tubes take place
Stems cells are present in meristematic tissue located between the xylem and phloem = called the vascular cambium
Stem cells of vascular cambium divide and differentiate into xylem and phloem, on either side of meristem
Uses of stem cells in research (Alzheimers)
Nerve cells in brain dies
Causes memory loss
Use stem cells to regenerate healthy nerve cells
Uses of stem cells in research (Parkinson’s)
Nerve cells that release chemical dopamine that controls movement is lost
Causes loss of control of movement
Stem cells used to regenerate dopamine producing cells
What is an organ
A group of different tissues that work together to perform a particular function
Different tissues that make up an organ (lungs)
Squamous
Ciliated
Vascular
Elastic connective
Different tissues that make up an organ (leaves)
Palisade
Epidermal
Xylem
Phloem
Different organs that make up an organ system (respiratory)
Trachea Lungs Mouth Nose Larynx Diaphragm
Different organs that make up an organ system (circulatory)
Heart
Veins
Capillaries
Arteries
