Chapter 6 - Cell division....

what is the cell cycle ?

A highly ordered sequence of events that takes place in a cell, resulting in the division of the cell, and the formation of two genetically identical daughter cells.

what are the phases that a eukaryotic cell cycle has ?

interphase, mitotic phase, cytokinesis

what is the interphase ?

period of the cell cycle between cell divisions

what is the interphase also known as ?

the resting phase

what happens during interphase ?

dna is replicated and checked for errors

protein synthesis occurs

mitochondria grow and divide increasing number in cytoplasm

chloroplasts grow and divide

so splitting of membrane bound organelles

what are the three stages of interphase ?

G1, S, G2

What is the G1 phase?

first growth phase

proteins from which organelles are synthesised are produced and organelles replicated

what is s phase ?

DNA replicated in the nucleus

What is the G2 phase?

the cell continues to increase in size, energy stores increase, duplicated dna checked for errors

what are the two stages of cell division ? + what are they ?

mitosis- nucleus divides

cytokinesis-cytoplasm divides and two cells are produced

What is the G0 phase?

-The name given to the phase when the cell leaves the cycle, either temporarily or permanently.

what are the reasons for g0 ?

differentiation - cell that becomes specialized to carry out a particular function is no longer able to divide

damaged dna - damaged cell can no longer divide and enters period of permanent cell arrest

senescent cells- as you get older the number of cells in g0 increase

why is vital to control the cell cycle ?

to ensure a cell only divides when it has grown to the right size, the replicated dna is error free and chromosomes are in the correct positions during mitosis

what are the control mechanisms of the cell ?

checkpoints

what do check points monitor ?

whether the process at each phase of the cell cycle have been accurately completed before the cell is allowed to progress into the next phase

what are the different checkpoints and where are they located ?

g1 - located at the end of the g1 phase

g2 - located at the end of the g2 phase

spindle assembly checkpoint - mitosis

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, DNA damage

what is the spindle assembly checkpoint ?

checkpoint is at the point in mitosis where all the chromosomes should be attached to spindle fibres

what is mitosis ?

ensures that both daughter cells produced when a parent cell divides are genetically identical so each new cell will have an exact copy of dna present in the parent cell

what are the four stages of mitosis ?

prophase, metaphase, anaphase, telophase

what happens during prophase ?

\-chromatin fibres begin to coil and condense to form chromosomes that will take up stain to become visible under microscope

\-protein microtubules form spindle shaped structures linking the poles of the cell

\-two centrioles migrate to opposite ends of the cell

\-spindle fibres attach to specific areas on the centromeres and start to move chromosomes to the centre of the cell

\-end of prophase nuclear envelope has disappeared

what are chromatin fibres ?

Complex made up of various proteins, RNA and DNA

what are centrioles ?

Cylindrical bundles of proteins that help in the formation of the spindle

what happens during metaphase ?

the chromosomes are moved by the spindle fibres to form a plane in the centre of the cell called the metaphase plate

what happens during anaphase ?

centromeres holding together the pairs of chromatids in each chromosome divide

the chromatids are separated - pulled to the opposite neds of the cell by spindle fibres

what is telophase ?

\-chromatids now called chromosomes again

\-nuclear envelope reforms around them

\-chromosomes start to uncoil and the nuclelous is formed

\-cytokinesis begins

what is cytokinesis ?

actual division of the cell into two cells

what is haploid ?

one set of chromosomes

what is diploid ?

two sets of chromosomes

What happens in sexual reproduction?

two sex cells (gametes) one from each parent fuse to produce a fertilised egg (zygote)

how many chromosomes do gametes (sex cells) contain ?

half the standard number of chromosomes in a cell so haploid - (23)

what are gametes formed by ?

meiosis

what is the difference between mitosis and meiosis ?

Mitosis produces four haploid cells whereas meiosis produces two diploid cells

Mitosis daughter cells are genetically identical whereas meiosis daughter cells are genetically different

No crossing over in prophase however there’s crossing over in prophase I

Mitosis has one cell division however meiosis has two cell divisions

Mitosis isn’t a reduction division however meiosis is a reduction divison

how many chromosomes does each gamete contain ?

half of the chromosome of each parent cell so haploid (23)

what is meiosis known as ?

reduction division

What are homologous chromosomes?

Chromosomes that have the same sequence of genes and the same structure

what are alleles ?

Different forms of the same gene

what is a locus ?

position of a gene or a specific sequence within a chromosome

How many divisions occur in meiosis?

two

what happens in meiosis I ?

reduction division

pairs of homologous chromosomes are separated into two cells

cells are haploid as they each cell only contains one full set of genes

what happens in meiosis II ?

the pairs of chromatids present in each daughter cell are separated

how many haploid cells in total during meiosis?

four

What happens in prophase I?

chromosomes condense

nuclear envelope disintegrates

nucleolus disappears

spindle formation begins

what is the difference between prophase 1 in meiosis and prophase in mitosis ?

recombination, and crossing over do not take place in mitosis.

In prophase, I of meiosis I, recombination, crossing over, and synapsis takes place.

what happens in metaphase 1 ?

same as metaphase in mitosis

1 difference is homologous pairs of chromosomes assemble along the metaphase plate instead of individual chromosomes

What is independent assortment?

Random distribution of homologous chromosomes

What does independent assortment result in?

genetic variation

How is anaphase 1 different from anaphase in mitosis?

the homologous chromosomes are pulled to the opposite poles and the chromatids stay joined together

chiasmata occurs during anaphase 1

what is chiasmata ?

points at which chromatids break and rejoin

what happens during anaphase I?

The homologous pairs of chromosomes are separated as microtubules pull whole chromosomes to opposite ends of the spindle

The centromeres do not divide

what happens in telophase I? (how much different is it from telophase)

essentially the same as telophase in mitosis

the chromosomes assemble at each pole

nuclear membrane reforms and chromosomes uncoil

what does the cell under go ?

cytokinesis and divides into two cells

what is the second stage of meiosis ?

meiosis II

what happens in prophase II ?

chromatids condense and become visible again

nuclear envelope breaks down and spindle formation begins

how does metaphase I differ from metaphase II ?

the bivalents assemble on the metaphase plate rather than individual chromosomes

is there more or less genetic variation in metaphase II?

due to crossing over the chromatids are no longer identical so there is independent assortment again and more genetic variation produced in metaphase II

how is anaphase II different from anaphase I ?

anaphase II results in the chromatids of the individual chromosomes being pulled to opposite poles after division of centromeres

what happens in telophase II ?

\-chromatids assemble at the poles of telophase II as in telophase of mitosis

\-the chromosomes uncoil and form chromatin again

\-nuclear envelope reforms

what does cytokinesis result in ?

results in division of the cells forming four daughter cells in total

in meiosis will the cells be haploid or diploid ?

haploid

what is the process that results in them being genetically different ?

crossing over and independent assortment

what can the organisation of a multicellular organism be summarised as ?

specialised cells ---> tissues ----> organs ---->organ systems----> whole organism

what are differentiated cells ?

Cells specialised to carry out specific functions

how are erythrocytes specialised to their function ?

they have flattened biconcave shape increasing their surface area to volume ratio

elastic membrane so it is flexible

high amounts of haemoglobin which can readily bind to oxygen

no nucleus present

why is large surface area to volume ratio essential ?

It means that there is a short diffusion pathway which is beneficial to their role of transporting oxygen around the body

why is it important erythrocytes are flexible ?

so that they are able to squeeze through narrow capillaries

what are neutrophils ?

white blood cells, play an important part in immune system

How are neutrophils specialised?

have multi-lobed nucleus to squeeze through small gaps to get to infection

large numbers of lysosomes which contain enzymes to destroy pathogens

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what are sperm cells and what is their function ?

male gametes and their function is to deliver genetic information to the female gamete

how are sperm cells specialised ?

they have tail or flagellum so capable of movement and contain many mitochondria to supply the energy needed to swim

the acrosome on the head of the sperm contains digestive enzymes which are released to digest the protective layers around the egg and allow sperm to penetrate

Name some specialised plant cells

palisade cells, root hair cells, pairs of guard cells

where are palisade cells present ?

mesophyll

How are palisade cells specialised?

the cells are rectangular box shapes which can be closely packed to form a continuous layer

thin cell walls increasing the rate of diffusion of carbon dioxide

large vacuole to maintain turgor pressure

where are root hair cells present ?

at the surfaces of roots near the growing tips

How are root hair cells specialised?

\-has a large surface area to absorb more water and mineral ions

\-thinner walls to shorten diffusion distance

\-permanent vacuole with concentrated cell sap to maintain water potential gradient

\-mitochondria for active transport of mineral ions

Where are pairs of guard cells located?

on the surfaces of leaves form small openings called stomata

what is tissue made up of ?

A collection of differentiated cells that have a specialised function so as a result each tissue is adapted to a particular function within an organism

what are the four main categories of tissues in animals ?

nervous tissue, epithelial tissue, muscle tissue, connective tissue

what is nervous tissue adapted to do ?

adapted to support the transmission of electrical impulses

what is the epithelial tissue adapted to do ?

cover the body surfaces both internal and external

what are muscle tissue adapted to do ?

contract

what is connective tissue adapted to do ?

either to hold other tissues together or as a transport medium

what are examples of specialised animal tissues ?

squamous epithelium, ciliated epithelium, cartilage muscle

How is squamous epithelium specialised?

has a flat appearance and very thin as its only one cell thick, its present when rapid diffusion across a membrane is essential

its forms lining of the lungs and allows rapid diffusion of oxygen into the blood

how are ciliated epithelium cells specialised ?

\-they have hair-like structures called cilia on one surface that move in a rhythmic manner

\-goblet cells that secrete mucus

how is cartilage adapted to is function ?

contains fibres, of the proteins elastin and collagen cartilage is a firm flexible connective tissue

what does muscle need to be able to do ?

to be able to shorten in length in order to move bones which in turn move different parts of the body

what are the different tissue in plants ? what is their function?

epidermis tissue which is adapted to cover plant surfaces

vascular tissue adapted for transport of water and nutrients

what is the epidermis ?

a single layer of closely packed cells covering surfaces of plants

usually covered by a waxy waterproof cuticle to reduce the loss of water

what is xylem tissue ?

a type of vascular tissue responsible for transport of water and minerals up plants

how is the xylem adapted ?

\-lignified cell walls : adds strength to withstand hydrostatic pressure

\-no end plates : allows the mass flow of water

\-bordered pits in wall : lateral movement of water

what is the phloem tissue ?

type of vascular tissue in plants responsible for the transport of organic nutrients

each organ system is....

composed of a number of organs working to carry out major function in the body

what are the three organ systems in animals ?

the digestive system, the cardiovascular system, the gaseous exchange system

what is the digestive system ?

takes in food breaks down the large insoluble molecules into small soluble ones and absorbs the nutrient in the blood

What is the cardiovascular system?

moves blood around the body to provide an effective transport system for the substance it carries

what is the gaseous exchange system ?

brings air into the body so oxygen can be extracted for respiration

what do all animal and plant cells begin as ?

undifferentiated / unspecialised

what are undifferentiated cells called ?

stem cells