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Biology Chapter 7 + 8
Terms in this set (68)
Why is cell division called a cycle?
Series of stages a cell progresses through as it grows and undergoes cell division.
Describe the relationship between parent cell and daughter cell.
A diploid parent cell divides by mitosis to produce two diploid daughter cells that are genetically identical to the parent cell. The parent cell is the original cell and the resulting cells are the daughter cells.
Name and describe the four phases (G1, S, G2, M and C) of the cell cycle. Describe what is meant by the G0 phase.
G1 - Checkpoint stage (Checks that conditions are favourable for cell division to take place and DNA to be replicated
S - Synthesis stage in which DNA is replicated
M - Mitosis - division of the DNA (genetic material)
G2 - Checkpoint stage (Checks that all chromosomes have been replicated)
G0 - Extended G1 phase - cell is neither undergoing cell division nor preparing to divide
Distinguish between mitosis and cytokinesis.
In Mitosis, diploid parent cell duplicates its DNA and localises chromosomes to the poles and new nuclear membranes reform ready for the cytoplasm to pinch into two whereas in cytokinesis, plasma membrane pinches in to divide the cytoplasm (cell volume) into two daughter cells.
Identify similarities and differences between cytokinesis occurring in plant and animal cells.
In animal cells, during cytokinesis, the plasma membrane pinches inwards and forms furrows that will split the parent cell into 2 separate daughter cells.
In plants cells, furrows don't appear, new cell plates are laid down to form new cell walls. In both cases, the plasma membrane divides.
Why is it essential for DNA replication to occur prior to cell replication?
Each daughter cell is genetically identical to the parent cell so the DNA must replicate so each of the two daughter cell has the same amount of DNA as the original cell.
Describe the stages involved in binary fission.
· DNA replication (DNA uncoils and duplicates)
· Growth phase
· Segregation of the DNA (DNA pulled to opposite poles of the cell)
· Splitting of the cell volume (Cell wall results, splitting the bacterium into two daughter cells each with coiled DNA)
Compare similarities and differences between binary fission and mitosis.
-Parent cell duplicates its genetic material (Chromosomes/single strand of circular DNA)
-Original parent cell will divide into 2 daughter cells
-Daughter cells are each genetically identical to the parent cell
-Mitosis occurs in Eukaryotic cells whereas binary fission occurs in Prokaryotic cells.
-Process of mitosis is more complex and takes longer than binary fission whereas process of binary fission is a very simple, rapid process resulting in exponential numbers of simple prokaryotic cells in a short amount of time
Name and describe the stages of mitosis.
(Interphase is the 'intermediate stage' between mitotic divisions)
Prophase - Nuclear membrane disintegrates, DNA is replicated, Chromosomes condense, chromosomes are now double stranded. Sister chromatids are joined at the centromeres. Centrioles migrate to the poles and constriction fibres start to form the spindle.
Metaphase -Double stranded chromosomes line up along the equator of the cell in no particular order.
Anaphase - Centromeres are pulled apart and chromatids migrate along the spindles towards opposite poles. Chromosomes are now single stranded.
Telophase -Nuclear membrane reforms, cytoplasm starts to divide as plasma membrane pinches in.
Cytokinesis occurs at the end of the mitotic stage once the DNA has been replicated and segregated. Cytokinesis results in the cell volume dividing into two.
Does mitosis take place in somatic or sex cells? Does mitosis produce somatic or sex cells?
In diploid somatic cells (body cells). Produces somatic cells.
Explain the role of centrioles and spindle fibres in mitosis.
The centrioles are small organelles responsible for making contractile spindle fibres.
Chromatids move along these fibres as they migrate to opposite poles of the cell during anaphase.
Explain the relationship between the terms replicated chromosome, chromatids and centromere. Draw an image to support your explanation.
Each Chromosome has another homologous chromosome that has the same chromosome number, length, and banding of genes (loci/position of genes). In diploid cells, chromosomes are found in pairs.
Chromatids refer to a chromosome that has undergone replication and consists of 2 chromatids
When chromosomes have replicated, the 2 strands are held together at the centromere. The chromatids are termed 'sister chromatids' when they are attached at the centromere.
Apoptosis is controlled, sequential, programmed cell death that enables the body to 'kill off' cells that are unwanted. It is an essential part of the cells growth.
Explain why apoptosis is important for maintaining life.
Certain cells are not needed by the body as the body grows. There is no need for these cells to grow and differentiate and the body destroys them. If apoptosis does not happen, cells will have the potential to divide and grow in an uncontrolled manner leading to masses of cells (eg. Cancer tumours)
Outline the sequence of events in apoptosis.
Apoptosis begins with the expression of a number of genes. This causes enzymes to shred the cell's DNA. The nucleus is broken down and the plasma membrane bulges outward, forming blebs. Apoptotic bodies form; they contain cell contents and are surrounded by a plasma membrane. Apoptotic bodies are cleaned up by phagocytes, which are part of the immune system.
State examples of cells that are likely to undergo apoptosis.
Webbing between human fingers and toes during embryo development.
Name the checkpoints in the cell cycle.
G1 phase, G2 Phase, mitosis checkpoint
Outline the purpose of the cell cycle checkpoints. Name and describe the role of each checkpoint
G1 checkpoint- Checks whether DNA is ok, there are enough resources for cell replication, enough proteins have been built and whether the environment is ok.
G2 checkpoint - Checks whether DNA has been replicated correctly, DNA replication is complete and enough proteins have been built.
Mitosis Checkpoint- Checks whether spindle fibres have been properly formed, the chromosomes are correctly orientated and all chromosomes are attached to the spindle fibres.
Outline the role of proto-oncogenes, oncogenes, p53 gene and tumour suppressor genes.
-Proto-oncogenes are normal cell genes that help the cell grow.
-If proto-oncogenes are mutated, they can turn into oncogenes that do not allow the cell to differentiate, instead they result in uncontrollable cell growth.
-P53 proto-oncogene is a tumour suppressor gene and prevents the formation of cell clumps (tumours) but this p53 gene can become a p53 Oncogene and result in cancer.
-Tumour suppressor genes reduce the rate of cell division and instead promote cell differentiation
Define mutagen. List and explain the types of mutagens.
A mutagen is any agent or factor that causes a change in the DNA.
There are chemical mutagens eg. carcinogens in cigarettes, biological mutagens eg. Virus, bacteria and physical mutagens eg. X-rays, radioactive substances, UV radiation.
A mutation is the results caused by this DNA sequence change and it results in a change in the protein that is produced from the DNA code.
Define the term stem cell.
Stem cells are undifferentiated cells. They have the potential to replicate and to develop into many different kinds of cells.
Explain the difference between totipotent, pluripotent and multipotent stem cells.
Totipotent cells - ability to form embryo (zygote is the first diploid cell) and the membrane that surrounds the embryo. The inner cell mass will then start to develop inside this membrane.
Pluripotent cells - capable of giving rise to MOST of the tissue of an organism but not all. It starts to develop the inner cell mass of the embryo.
Multipotent cells - capable to give rise to specific cells with very specific functions eg. muscle and blood cells.
Differentiation - cells progress through a developmental process that will see them develop in their structure to perform a specific function.
Somatic cells of an organism are all expected to contain the same genetic information, yet these cells are likely to vary in their structure and function. Refer to 'differentiation' to explain this.
'Somatic' refers to a group of cells that are diploid and found throughout the body. In each specific cell, certain genes are turned on that code for certain proteins and this will allow that particular cell to develop uniquely compared to another somatic cell that has different genes 'turned on'
Name the three primary germ layers. List structures formed by each primary germ layer.
Ectoderm-Epithelium of alimentary canal and its glands,
Mesoderm-Skeletal, smooth and cardiac muscles,
Endoderm-Epidermis of skin
Distinguish between the zygote, embryo and foetus.
A zygote is the first diploid cell formed from the fusion of 2 gamete cells, 2 months on development after fertilisation it is named an Embryo and the developing baby from 2 months is named Foetus.
List the three sources of stem cells.
1. Umbilical cord blood and placental stem cells
2. Embryonic stem cells
3. Adult stem cells
Describe advantages and/or disadvantages associated with the use of each different stem cell source.
1. Umbilical cord blood and placental stem cells -
Advantages: easy to get, easy to store, no harm to the mother or the child
Disadvantage: Multipotent eg. blood cells only make blood cells.
2. Embryonic stem cells -
Advantages: Pluripotent so have the ability to differentiate into a wider range of cells than that from adult stem cells.
Disadvantages: frozen embryos, ethical issues involved as embryos are discarded afterwards.
3. Adult stem cells -
Advantages: a patient's own cells can be used to treat their own disease and so rejection is reduced.
Disadvantage: Multipotent eg. blood cells only make blood cells.
Describe similarities and differences between stem cells and other body cells.
· Stem cells are undifferentiated cells and have not yet started allow their path of specialisation whereas body cells have already undergone some kind of specialisation to perform a specific function.
· Stem cells are capable of repeated cell division through mitosis for very long periods of time.
. Similarities are that both these types of cells are diploid (somatic cells) and replicate by mitosis to increase their numbers.
If cells become cancerous, what does this mean?
Uncontrollable cell growth without the cells becoming differentiated to perform a specific function.
Distinguish between the terms DNA replication, nuclear division and cytokinesis.
DNA replication involves the replication of the cells chromosomes and occurs during interphase in the S phase, Nuclear division involves dividing the genetic material in the nucleus through telophase whereas cytokinesis involves dividing the cytoplasm and occurs immediately after mitosis.
Name three regions of the body where mitosis is likely to occur at a fast rate. Explain your choice.
Skin, lining (epithelial tissue) of the stomach, inside lining (epithelial tissue) of the mouth
Will the rate of mitosis be the same in all regions of the body? Explain.
Where there are regions of high activity, cells will need to be repaired and replaced more frequently so the rate of mitosis will be higher.
During the cell cycle, the amount of nuclear DNA is likely to change. Describe when and for what reasons, changes are likely to be observed.
-During Prophase the amount of DNA will double as the chromosomes replicate to become double stranded.
-During Telophase the amount DNA will return to the original amount as the cell divides into two again.
Reproduction is the creation of a new generation of single cells, single celled organism or multicellular organism.
Define asexual reproduction
Asexual reproduction is a form of reproduction in which offspring are produced from a single parent.
Define sexual reproduction.
Sexual reproduction is a form of reproduction in which offspring are produced from 2 parents and involves a mixing of the parent's genetic information.
List and explain differences and similarities between asexual and sexual reproduction.
They both results in more offspring that the parent number and each original parent cell divides to produce more daughter cells.
-In asexual reproduction, only one parent is involved whereas in sexual reproduction two parents are involved.
-In asexual reproduction, genetic information is from just one parent whereas in sexual reproduction Genetic information is combined from 2 parents.
-asexual reproduction results in organisms that are genetically identical clones of the parent cell whereas asexual reproduction results in organisms that show genetic variability from each other and from the parents.
-Asexual reproduction is quick and uncomplicated and allows organisms to maximise favourable conditions whereas sexual reproduction is slower, more complex process and allows organisms to adapt to a changing environment.
-Involves the process of mitosis whereas sexual reproduction Involves the process of meiosis.
List and describe advantages and disadvantages for each of asexual and sexual reproduction.
-Asexual reproduction is quick and uncomplicated and allows organisms to maximise favourable conditions
-Do not need to find a mate
-No ability for genetic variation so if the environment is not good, they cannot adapt.
-Sexual reproduction is slower, more complex process and allows organisms to adapt to a changing environment
-Allows genetic variation so may allow survival of a species
-Need to invest energy in finding a mate
Describe the main methods of asexual production (Fission, Budding, Vegetative propagation, Spore formation) and give examples.
Division of the cell by mitosis, producing two daughter cells. eg Amoebae
An outgrowth of the parent detaches and grows into a new individual. eg Hydra
Part of a plant is detached and grows into a new individual. eg Runners of strawberry plants
Creation of hardy capsules which contain DNA. In times of rain the spores can grow into new individuals. eg Fungi and ferns
Explain why offspring produced from asexual reproduction are considered to be genetic clones of their parents, yet offspring produced from sexual reproduction are not.
In asexual reproduction offspring are clones of the parent and share identical genetic information whereas in sexual reproduction the offspring are a combination of the genetic information contributed from 2 parents.
Many plants are able to reproduce both sexually and asexually. Describe the advantages this offers to the species that are able to do so.
In favourable conditions and where plants are spaced out from each other, asexual reproduction is quick, results in large numbers of organisms being produced and does not require another plant. During unfavourable conditions, if sexual reproduction occurs, the chance of survival of the species is increased due to genetic variation.
Explain why fertilization is NOT required in asexual reproduction.
Asexual reproduction only involves a diploid parent dividing to produce diploid offspring. Meiosis does not occur so fertilisation involving haploid gametes does not take place. Only one parent cell or organism is involved. There is no fusion on gametes.
Process whereby a whole organism is produced that is genetically identical to the parent. Only one parent is involved in cloning.
Describe the process involved in embryo splitting
Egg cells are are removed from the donor female and fertilised in vitro by sperm from the male. After the fertilised egg has been divided, the coat around the 2 cells that promotes cell division is removed and the 2 cells are separated. Each cell is then given an artificial coating that promotes cell division. Blastocysts are implanted into the surrogate mothers.
Describe the process involved in nuclear transfer.
It involves removing mature donor somatic cells from a mature animal and a recipient egg cell from another mature animal of the same species. When the donor cells become inactive, the nucleus of the recipient egg cell is removed. The donor cell's nucleus is electrically fused with the 'hollow' egg. After being cultured for 1 week, cell division is activated and the developing blastocyst is surgically implanted.
For each of the processes (embryo splitting, nuclear transfer. ), explain who the offspring are likely to be 'clones' of.
Embryo splitting - offspring are clones of each other.
Nuclear transfer - offspring is genetically identical to the nuclear donor NOT identical to the surrogate that carries the embryo.
Describe advantages and disadvantages of using cloning in agriculture.
· increases the number of breeding animals with naturally desirable traits
· conserves rare or endangered species
· does not allow for genetic variability compared to the parent
Describe advantages and disadvantages of using cloning in horticulture.
· mass production of plants
· if environmental conditions change, there is no variation for adaptation to a changing environment
compare somatic cells and gametes of humans in terms of : Number of chromosomes? homologous chromosomes present? cells haploid or diploid? the cell process most commonly used to produce these cells?
List and describe the stages of meiosis.
Prophase I-Chromosomes condense and nucleus disappears, spindle forms with centrioles at opposite ends. Homologous chromosomes go through synapsis and cross over.
Metaphase I-The nuclear envelope breaks down and the homologous chromosomes move together to the equator of the spindle. Spindle fibres attach to the centromeres of each homologous pair.
Anaphase I-spindle fibres retract towards the poles, pulling the maternal and paternal chromosomes of homologous pairs towards opposite poles of the spindle.
Telophase I-The spindle breaks down, the cell starts to seperate across its middle and nuclear envelope form around the 2 nuclei.
Cytokinesis I-The cell's cytoplasm (cell volume) is divided and 2 haploid cells are formed.
Prophase II-Chromosomes condense and nucleus disappears, spindle forms with centrioles at opposite ends. New spindles form.
Metaphase II-Chromosomes move to the equator of the spindle and spindle fibres attach to the centromere of each chromosome.
Anaphase II-Spindle fibres retract towards each pole and the chromatids seperate and move apart from each other.
Telophase II-The spindle breaks down, the cell starts to seperate across its middle and nuclear envelope form around the nuclei.
Cytokinesis II-The cell's cytoplasm (cell volume) is divided and 4 haploid cells are formed.
Compare similarities and differences for prophase I and prophase II
In Prophase I, there is only 1 cell present whereas in prophase II there are 2 cells present.
The chromosomes have homologous pairs in prophase I whereas they are no longer paired by prophase II. Therefore chromosomes are diploid in prophase I whereas they are haploid in prophase II. There's crossing over in prophase I whereas there's no crossing over in prophase II.
Both stages are preparing the cells for division.
Compare similarities and differences for metaphase I and metaphase II
In metaphase I, there is only 1 cell present whereas in metaphase II there are 2 cells present. The chromosomes in metaphase I are paired with their homologous pair whereas in metaphase II, there are single chromosomes. Therefore chromosomes are diploid in metaphase I whereas they are haploid in metaphase II.
In both stages, chromosomes move up to the equator of the spindle and spindle fibres attach to the centromeres of the chromosomes. Both stages are preparing the cells for division.
Compare similarities and differences for anaphase I and anaphase II
In anaphase I, there is only 1 cell present whereas in anaphase II there are 2 cells present. In anaphase I when the spindle fibres retract towards each end of the pole, they pull double-stranded chromosomes towards each end of the pole whereas in anaphase II, the spindle fibres pull a chromatid towards each end of the pole.
In both stages, chromosomes are pulled away to each end of the pole. Both stages are preparing the cells for division.
Meiosis is known as a reduction division. Explain what this means.
Each division results in a halving of the genetic material.
Meiosis 1 results in a separation of homologous pairs but the chromosomes are still double stranded (halving of the chromosome number - double stranded haploid number)
Meiosis 2 reduces the double stranded chromosomes to single stranded chromosomes (single stranded haploid number)
Explain the process of crossing over.
Double stranded chromosomes pair up side by side with their homologous partner.
They coil around each other and chromatids break and rejoin sometimes rejoining with other chromatids.
When is crossing over likely to take place?
What is the biological advantage of crossing over?
Results in recombinant DNA (combination of paternal and maternal genetic information)
Allows for genetic variation in the gametes produced for sexual reproduction.
Define the term homologous chromosomes.
Pair of chromosomes that have the same size, shape and banding/genes at the same locations (loci along the chromosome)
Define the term bivalent.
when 2 homologous chromosomes are joined together and are visible in the cell during Prophase.
Define the term synapsis.
The pairing of the homologous chromosomes
Define the term recombinant chromosomes.
Offspring that have different combinations of DNA than their parents due to mixing of the genes
Compare mitosis and meiosis for human cells. Where it occurs? Why it occurs? What cells undergo it (gamete or somatic cells)? What cells are produced (gamete or somatic cells)? How many cells are produced per cycle? How many chromosomes are in the parent cell? How many chromosomes are in the daughter cells? Are the daughter cells haploid or diploid? Are the parent cells haploid or diploid?
Where it occurs?
Everywhere in the body-Only in reproductive organs (ovaries and testes)
Why it occurs?
Growth, repair and replacement of cells in the body-To produce gametes (sex cells)
What cells undergo it (gamete or somatic cells)? Somatic cells-Germ cells (reproductive cells)
What cells are produced (gamete or somatic cells)?
Somatic cells-Gamete cells
How many cells are produced per cycle?
How many chromosomes are in the parent cell?
2n = 46-2n = 46
How many chromosomes are in the daughter cells?
2n = 46-n = 23
Are the daughter cells haploid or diploid?
Are the parent cells haploid or diploid?
Explain why children of the same parents do not inherit identical chromosomes (except for identical twins).
Due to crossing over during Prophase 1 in Meiosis where homologous chromosomes synapse and exchange sections of genetic information between maternal and paternal chromosomes and due to independent assortment of chromosomes in Anaphase 2 into the haploid sex cells, siblings display genetic differences to each other and to their parents.
factor that will be measured in an experiment.
a factor in an experiment that remains constant.
variable that is manipulated.
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