Cell division, cell diversity and cellular organisation Flashcards
What is the cell cycle?
a highly ordered sequence of events that takes place in a cell, resulting in division of the cell, and the formation of two genetically identical daughter cells
What are the two main phases of the cell cycle?
- interphase
- mitosis
What is interphase divided into?
G1, S and G2
What is mitosis divided into?
Prophase, metaphase, anaphase, telophase
What happens during interphase?
- DNA is replicated and checked for errors
- protein synthesis
- mitochondria and chloroplasts grow and divide, increasing in number
- normal metabolic processes occur eg respiration
What happens at G1?
- cell growth
- cellular components
- protein synthesis
What happens in the S phase if interphase?
Each of the chromosomes are duplicated
What happens at G2?
- cell size increases
- the cell checks the duplicated chromosomes for errors, making any repairs that are needed
- energy store increases
What happens at cytokinesis?
Cytoplasm divides
What happens at G0?
When the cells leave the cycle either temporarily or permanently
Why do cells enter G0?
- differentiation
- cells may be damaged
- apoptosis
Give an example of a cell that can be stimulated to go back into the cell cycle after G0?
Lymphocytes
Why is it important that the cell cycle is controlled?
To ensure the fidelity of cell division
What are the roles of checkpoints in the cell cycle?
They monitor and verify whether the process at each phase has been accurately completed before the cell is allowed to progress to the next phase
What does the G1 checkpoint check for?
- cell size
- nutrients
- growth factors
-DNA damage
What does the G2 checkpoint check for?
- cell size
- DNA replication
What does the spindle assembly checkpoint check for?
Chromosomes attachment to spindle
Why do cells divide by mitosis?
- growth
- repair
- asexual reproduction
What does asexual reproduction?
- fungi
- plants
- some animal cells
What is a centromere?
A structure on a chromosome that allows two chromatids to attach to each other or to the spindle during cell division
What is a chromatid?
One of two halves of a replicated chromosome
What is a homologous chromosome?
A pair of chromosomes of the same length and carrying the same genes in the same positions- one is maternal and one is paternal
What happens before prophase?
DNA combines with histone proteins to form a dense complex chromatin
What happens during prophase?
- chromatin fibres coil and condense to form visible chromosomes
-nucleolus disappears - nuclear envelope starts to break down
- microtubules form the spindle that links the poles of the cell
- spindle attaches to centromere to move chromosomes to centre of cell
- nuclear envelope disappears
What happens during metaphase?
- spindle fibres pull the chromosomes by their centromeres to align them around the equator of the cell
- this is called the metaphase plate
- centromeres replicate
What happens during anaphase?
- centromeres holding the sister chromatids together divide
- the chromatids separate
- chromatid acids are dragged to opposite ends
What happens during telophase?
- chromatids reach the poles and bunch together
- now called chromosomes
- nuclear envelope forms around each group
What happens after mitosis (cytokinesis)?
- divides cell into two separate cells at end of telophase
- animal cells form a cleavage furrow, where the cytoskeleton pulls the plasma membrane inwards until it fuses
- plant cells cannot form a cleavage furrow due to the cell walls
- at the metaphase plate the Golgi vesicles fuse with each other and the plasma membrane to create a cell division
- new sections of cell wall must then form
What is meiosis?
Type of cell division used to produce gametes
What is meiosis used for?
To halve chromosome number in preparation for sexual reproduction
What does meiosis result in?
Haploid cells containing N chromosomes (e.g 23 for humans)
Diploid cells containing 2N chromosomes (e.g 46 for human)
What happens in meiosis 1?
- divide the homologous pairs of chromosomes
- creates two haploid cells
What happens in meiosis 2?
- divides the sister chromatids
- creates 4 haploid cells form
What happens in early prophase 1 in meiosis?
- chromosomes replicated
- starting to become more visible
- centrioles replicate
- nucleus disappears
What happens in mid prophase 1 in meiosis?
- chromosomes are fully condensed
- homologous chromosomes pair up
What happens in late prophase 1 in meiosis?
- crossing over begins (of chromosomes)
- prepare to break and reconnect to another chromatid
- occurs at chiasmata
- nuclear envelope disintegrates
- spindles form
What happens in metaphase 1 in meiosis?
- chromosomes line up at equator randomly
- centromere attaches to spindles
- allows for independent assortment
- chromosomes separate randomly
What happens in anaphase 1 in meiosis?
- while chromosomes move to opposite poles
-crossing over is compete- chiasmata separates
What happens in telophase 1 in meiosis?
- nuclear envelope reforms
- ends up with 2 nuclei - chromosomes uncoil to form chromatin
What happens in cytokinesis in meiosis 1?
Separates cytoplasm to give two haploid daughter cells
What happens in prophase two in meiosis?
- chromosomes condense
- nuclear envelope starts to break down
- centrioles replicate
- spindle starts developing
What happens in metaphase two in meiosis?
- chromosomes line up at equator
- spindle fibres attaches to centromere
- independent (random) assortment of chromatids
What happens in anaphase two in meiosis?
- centromeres divide- each chromatid is called a chromosome
- chromosomes pulled to opposite poles
- randomly segregated
What happens in telophase two in meiosis?
- chromosomes uncoil
- nuclear envelope reforms
- each nucleus has a chromatid from original homologous pairs
What happens in cytokinesis after meiosis two?
Two more daughter cells from each division= 4 haploid cells in total (not genetically identical)
Does mitosis have single or double division of chromosomes?
Single
Does meiosis have single or double division of chromosomes?
Double
Does mitosis have single or double division of nucleus?
Single
Does meiosis have single or double division of nucleus?
Double
What happens to the number of chromosomes in mitosis?
Stays the same (haploid)
What happens to the number of chromosomes in meiosis?
Halves (diploid)
Do homologous chromosomes come together in mitosis?
No
Do homologous chromosomes come together in meiosis?
Yes
Are chiasmata formed in mitosis?
No
Are chiasmata formed in meiosis?
Yes
Does crossing over happen in mitosis?
No
Does crossing over happen in meiosis?
Meiosis 1- yes
Meiosis 2- no
Are daughter cells identical to parent cells in mitosis?
Yes
Are daughter cells identical to parent cells in meiosis?
No
How many daughter cells are formed in mitosis?
2
How many daughter cells are formed in meiosis?
4
Do chromosomes form a double or single row at the equator in mitosis?
Single
Do chromosomes form a double or single row at the equator in meiosis?
Double (meiosis 1)
Single (meiosis 2)
What moves to opposite poles in mitosis?
Chromatids
What moves to opposite poles in meiosis?
Chromosomes (meiosis 1)
Chromatids (meiosis 2)
what are specialised cells?
cells that have gone through differentiation to carry put a specific role
what are erythrocytes?
red blood cells
what are adaptations of erythrocytes and what is their purpose?
- has flattened biconcave shape which increases surface area to volume ratio
- essential for role of transporting oxygen around the body - in mammals, they don’t have a nuclei which increases space available for haemoglobin
- flexible so can fit through tight capillaries
where are erythrocytes found?
blood vessels- arteries, veins, capillaries
what are neutrophils?
type of white blood cell
what do neutrophils play a role in?
the immune system
what are adaptations of neutrophils?
- multi-lobed nucleus which makes it easier for them to squeeze through tight gaps to get to the site of infections
what does granular cytoplasm contain in neutrophils?
lysosomes that contain enzymes used to attack pathogens
what are sperm cells?
male gametes
what is the function of sperm cells?
to deliver genetic information to the female gamete, the ovum
what are some adaptations of the sperm cell?
- have a flagellum to aid movement
- contain many mitochondria to supply energy for swimming
- the acrosome in the head of the sperm contains digestive enzymes
where are palisade cells found?
in the mesophyll and contain chloroplasts to absorb large amounts of light for photosynthesis
what are some adaptations of palisade cells?
- cells are rectangular which can be closely packed to form a continuous layer
- they have thin walls, increasing rate of diffusion of CO2
- large vacuole to maintain turgor pressure
where are root hair cells found?
at the surfaces of roots near the growing tips
what are some adaptations of the root hair cell?
they have long extensions called root hairs which increase the surface area of the cell
- this maximises uptake of water and minerals from the soil
where are guard cells found?
in pairs on the surface of leaves from small openings called stomata
what are guard cells necessary for?
carbon dioxide to enter plants for photosynthesis
what are some adaptations of guard cells?
- when guard cells lose water and become less swollen as a result of osmotic forces, they change shape and the stomata closes to prevent further water loss from plants
- cell wall is thicker on one side
what is the function of a neurone?
transmits electrical impulses around the body
what are adaptations of a neurone?
- has a long thin structure which increases the speed of nervous reactions
- the structure of the dendrite increases the surface area for synapses with other nerves
- the myelin sheath insulates the axon which increases the speed of impulse transmission
what is the function of the squamous epithelial cell?
provides thin exchange surface for tissues which is found in areas that require a smooth flow of liquid
what are some adaptations of the squamous epithelial cell?
- thin walls of tissue which makes gas exchange easier as it creates a shorter distance for diffusion
- has a smooth flat structure which increases surface area
what is the function of egg cells?
for female reproduction
what are some adaptations of egg cells?
- lots of cytoplasm which supports many cell divisions that occur within it
- has a haploid nucleus which contains 1/2 the genetic material for fertilisation
what are tissues?
a collection of different cells that work together to carry out a particular function
what are the four main categories of tissues?
- nervous tissues
- muscle tissues
- epithelial tissues
- connective tissues
what are organs?
a group of specialised tissues that work together to carry out a particular function
what is an organ system?
a collection of organs working together to carry out a particular function
what are the cells/components present in cartilage?
- fibres of elastin and collagen
- chondrocyte cells
- extracellular matrix
what is the role of cells/components in cartilage?
- it is a connective tissue
- elastin- returns shape to normal after contraction
- collagen- strength and structure
- chondrocyte cells produce extra-cellular matrix
what cells/component are present in squamous epithelium?
squamous epithelial cells
what is the role of cells/components in squamous epithelium?
- cover body surfaces
- low friction surface
- alveoli inside blood vessels
what cells/component are present in muscles?
- muscle fibres (myofibrils)
- connective tissues
what is the role of cells/components in muscles?
- myofibrils- contracting units
- connective tissues- joins them together
what cells/component are present in ciliated epithelium?
- ciliated epithelial cells
- goblet cells
what is the role of cells/components in ciliated epithelium?
- found in trachea and fallopian tubes
- ciliated cells- cilia move rhythmically
- goblet cells- make mucus
what cells/component are present in plant epidermis tissue?
- epidermal cells
- guard cells
- has a waxy cuticle
what is the role of cells/components in plant epidermis tissue?
- epidermal cells pack close together
- guard cells open and close stomata
- waxy cuticle reduces water loss
what cells/component are present in phloem?
- sieve tube elements
- companion cells
- sieve plates
what is the role of cells/components in the phloem?
- companion cells load sucrose into the phloem
- sieve plates allow dissolved sugars to be transported
what cells/component are present in xylem?
- vessel elements
- lignin
what is the role of cells/components in the xylem?
- the lignin is impermeable to water which adds strength
- tracheid- sealed off sections- has pit which allows lateral movement of water
- transport water and mineral ions
what is blastocyst?
after 7 days of development of an embryo, there is a mass of cells
what is potency?
the ability of a cell to differentiate into different cell types
what is a meristem?
type of tissue where stem cells are found in a plant
what is pluripotent?
stem cells that can form all tissue types, but not whole organisms
where are pluripotent cells found?
in embryos
what is totipotent?
stem cells that can differentiate into any type of cell
what is multipotent?
stem cells that can form a range of cells within a certain type of tissue
when a cell becomes specialised can it still divide?
no-they lose the ability
which areas are stem cells already being used in?
- burn treatment
- drug trials
- development/biology
what is developmental biology?
the study of changes that occur in development of multicellular organisms
suggest why the speed of division needs to be controlled in stem cells?
- too slow leads to aging
- too fast leads to tumour development
give a for argument for the use of stem cells?
range of treatments potentially available
give an against argument for the use of stem cells?
ethics issue- main source of embryonic stem cells would have been from embryos
how could stem cells help heart disease?
can replace damaged cardiac cells
how could stem cells help Parkinson’s disease?
can replace dopamine producing cells
how could stem cells help Alzheimer’s disease?
replacing cells that have been damaged by a protein
how could stem cells help spinal injuries?
replaces nerve cells
what are the stages in the mitotic phase?
mitosis and cytokinesis
what is mitosis?
refers to nuclear division
what has to happen before mitosis can occur?
all the DNA in the nucleus is replicated during interphase
each DNA molecule is converted into two identical DNA molecules, called chromatids
how can you view mitosis?
- using a light microscope
- can be obtained from growing root tips of plants
how are root tips prepared to view mitosis?
they are treated with a chemical which allows the cells to be separated, then they can be squashed to form a single layer of cells on a microscope slide
what forms around the middle of an animal cell in mitosis?
cleavage furrow
why do plant cells not have a cleavage furrow form?
they have cell walls so it is not possible
what happens in a plant cell during mitosis instead of a cleavage furrow forming?
vesicles from the Golgi begin to assemble in the same place as where the metaphase plate was formed
the vesicles fuse with each other and the cell surface membrane, dividing into two
where in plants are stem cells present?
meristematic tissue (meristems)
where can you find embryonic stem cells?
present at a very early stage of embryos development and are totipotent
where can you find adult stem cells?
present throughout life from birth
found in specific areas such as bone marrow
what are some examples of specialised tissues in animals?
- squamous epithelium
- ciliated epithelium
- cartilage
- muscle
what do muscles do?
shorten in length in order to move bones, which in turn move the different types of muscle fibres
what are the types of tissues in plants?
- epidermis
- vascular
