biology sac 2

Somatic cell

A normal body cell, as compared with a germ line cell from which a gamete ie, a sperm or an ovum is derived

Prokaryote cells A- divide by binary fission B- include yeasts, bacteria and Protists C- have a single stranded DNA molecule D- show a defined internal structure

A- divide by binary fission

The sex cells of algae and fern are called spores. They are produced by A- meiosis B- mitosis C- binary fission D- parthenogenesis

A- meiosis

Compared to small cells large cells have more trouble A- moving needed materials in and waste products out B- making cyclin proteins C- producing daughter cells D- dividing

A- moving needed materials in and waste products out

The cell theory/ derivation of cells

All living organisms are composed of cells (and the product of cells) The cell is the basic unit of structure, organisation and reproduction in organisms Cells come from preexisting cells

Mutagen

An agent that can induce or increase the frequency of mutation in DNA. For example, ultraviolet light (UV), X-rays, and nuclear radiation. Cancer causing agents are referred to as carcinogens. There are three types of carcinogens: physical, chemical and biological

Application of cloning in agriculture and horticulture

Animal cloning like other types of cloning is used to increase the number of breeding animals with naturally occurring desirable traits. This allows for the rapid spread of these characteristics through the herd. The cloning of farm animals for food production is already under way in a number of countries. When a large number of plants or species of an organism are produced that are genetically identical, they are left vulnerable to pest and disease infestation.

As a cell becomes larger it's A- volume increases but it's surface area stays the same B- volume increases faster than its surface area C- surface area increases faster than its volume D- surface area stays the same but it's volume increases

B- volume increases faster than its surface area

Binary fission

Binary fission is a form of asexual reproduction that involves division of the parent body into two fairly equal parts to produce two identical cells, in terms of their chromosomal DNA. Because the plasmids within the cell reproduce independently of themselves, each cell will have a different number of plasmids. Binary fission in prokaryotes- bacteria- no membrane bound organelles, no membrane bound nucleus. DNA contained in one singular chromosome. Binary fission is fast, and only requires a single organism to reproduce. However the only source of genetic variation is mutation.

All of the following are problems that growth causes for cells except A- expelling wastes B- DNA overload C- too much oxygen D- obtaining enough food

C- too much oxygen

Genetic control of the cell cycle

Cancer cells do not respond normally to the body's control mechanisms. Cancer cells may have an abnormal cell cycle control system. Abnormal activities may be due to two types of genes which regulate the cell cycle: Proto-oncogenes and tumour suppressor genes. Recent advances in understanding the cell cycle and cell cycle signalling have led to advances in cancer treatment

Where does mitosis take place in animals?

Cells and tissues (somatic cells)

Haploid

Cells which have only one kind of each chromosome

Diploid

Cells which have pairs of homologous chromosomes

Cloning

Cloning is the process of making an identical copy of an original. Genetic cloning involves making a copy of a gene through the use of recombinant technology. Biological cloning involves cloning an entire organism- that is reproductive cloning

Explain why the process of crossing over in meiosis is biologically important.

Crossing over results in the swapping of sections of DNA along the chromatids. Sometimes the chromatids rejoin back to the same chromatid with no crossing over; that is, they have the same sequences of DNA as previously. The amount of crossing over varies between species and within species between different homologous chromosomes. The end result of crossing over is the production of gametes with new parental combinations of DNA. This is an important source of genetic variation.

Cuttings/tissue culture (cloning)

Cuttings is similar to vegetative propagation except doesn't occur naturally (artificial form of asexual reproduction) Cutting of a plant is buried in soil and grows into a new plant Cuttings may be used by gardeners when a plant has a desirable characteristic they want to keep Tissue culture is when scientists take plant tissue into a laboratory and grow it in a nutrient medium where it will grow plants from the tissue samples. Micropropagation is the method used to produce clones of a plant, often scaled up to mass production.

Briefly state the biological significance of the process of meiosis

During meiosis, when homologous chromosomes pair and then move to different daughter cells independently of each other, gametes with many different combinations of parental chromosomes are possible. This is important in a changing environment as some of the new organisms may turn out to be better adapted to the new conditions due to their different genetic makeup.

Distinguish between embryonic stem cells and adult stem cells with respect to their potency

Embryonic stem cells are pluripotent and are derived from the inner cell mass of blastocysts and can give rise to many different types of specialised cells. Blastocysts are 3-5 day old embryos. Adult stem cells are multipotent and are undifferentiated cells obtained from tissues (eg brain, bone marrow, fat and liver) in adults, children and umbilical cord blood. These stem cells can give rise to the same type of tissue as where they were taken from.

How does binary fission in unicellular eukaryotes differ from that of prokaryotes.

Fission in unicellular eukaryotes involves mitosis and cytokinesis where as binary fission in prokaryotes does not. Binary fission is not a form of mitosis as it involves prokaryotes which don't have a true nucleus like eukaryotes.

Anaphase 1

In anaphase 1, homologous chromosomes separate. As they pull apart points of crossing over are visible as chiasmata. One member of each homologous pair migrated to each pole of the cell.

Anaphase II

In anaphase II, centromeres divide and chromatids separate and move to opposite poles of each cell

Explain why embryo splitting is different from nuclear transfer

In embryo splitting, egg cells are removed from the donor female and fertilised in vitro by sperm from the male. The fertilised egg splits and two or more embryos are created with identical DNA (or nearly identical). Nuclear transfer involves removing mature donor somatic cells from a mature animal and a recipient egg cell from another mature animal of the same species. The DNA is extracted from the nucleus of the somatic cell and inserted into the prepared egg. The new cell is then induced to divide thereby commencing the development of an embryo. After several days, the dividing embryo is then placed into the womb of the recipient and allowed to develop to term. Dolly the sheep was the first organism to be cloned by somatic cell nuclear transfer after 276 attempts.

Metaphase 1

In metaphase 1, homologous chromosomes pairs align on the equator of the spindle. They remain attached at crossing over points. Alignment is random, meaning there are many potentially different arrangements of the homologous pairs.

Metaphase II

In metaphase II, paired chromatids align along the equator of the spindle

Why are there ethical issues in the use of embryonic stem cells in research and medicine?

In order to obtain embryonic stem cells, an embryo is not only deliberately created but then destroyed within 3-5 days which appears unethical to many people.

Prophase 1

In prophase 1, the chromosomes condense, the nucleolus disappears and a spindle forms with centrioles, if présent, at opposite ends. Homologous chromosomes lie side by side, in a process known as synapsis. A pair of homologous chromosomes, one maternal and one paternal, is now called a bivalent. As prophase proceeds, homologous chromosomes may coil around each other intimately. Later, they move slightly apart but the chromatids remain in contact at certain points called chiasmata. At these contact points, crossing over and recombination occurs between the homologous chromosomes.

Prophase II

In prophase II, the nuclear membrane breaks down, centrioles divide again and the spindle reforms

Telophase 1

In telophase 1, the nuclear membrane begins to reform. The newly forming nuclei have only one member of each homologous pair (n) but each chromosome still consists of two chromatids. Cytokinesis, the division of the cell and cytoplasmic contents completes the first stage of meiosis.

Telophase II

In telophase II, the spindle breaks down, nuclear membranes begin to reform and cytokinesis occurs. Four gametes are formed. All four of these gametes are different. Each is a haploid cell (n), containing only two chromosomes, one member of each homologous pair. Usually in females three of the nuclei are broken down and just one survives in the newly formed ovum.

How does indépendant assortment increase the variation in gametes

Indépendant assortment is the random alignment and distribution of chromosomes during meiosis. During the first stage of meiosis, replicated homologous chromosomes pair up along the middle of the cell. The way the chromosomes pair up is random resulting in different combinations in the gametes.

Interkinesis

Interkinesis is a phase between divisions. This is very brief in most organisms and absent in some organisms. No replication occurs

Meiosis 1 premeiotic interphase

Meiosis begins with a diploid (2n) cell. Chromosomes are thin threads, replication of chromosomes occur and centriole divides. In human cells 2n= 46

Meiosis

Meiosis is a two-phase type of cellular division in which the chromosome number of a cell is halved to the haploid number; meiosis is the basis of gamete formation (sperm and ova). In the first division of meiosis, each chromosome of a pair separates and goes to each end, or pole of the cell. In the second division, the chromatids of each chromosome separate from each other. Four gametes are which are haploid are produced, each carrying half the original number of chromosomes.

Describe the roles of mitosis in the human body

Mitosis produces two identical daughter cells from a parent cell. This characteristic allows the body to produce cells to heal itself when it is damaged, and is also responsible for the production of the cells required for growth.

Why does multiple fission produce offspring more rapidly than simple binary fission

Multiple fission involves the nucleus dividing repeatedly before the final division of the cytoplasm to produce many new cells rather than dividing into only two cells. Repeated cycles of multiple fission rapidly produce large numbers of offspring.

Explain the advantage of multiple fission to an intracellular parasite such as Plasmodium.

Multiple fission results in rapidly producing large numbers of offspring therefore it is advantageous for an intracellular parasite like Plasmodium because it can quickly infect an organism.

Multipotent stem cells

Multipotent stem cells can develop into more than one of the cell types that make up the body but not all cell types. For example, blood stem cells and bone marrow stem cells.

New research has produced pluripotent stem cells from differentiated adult cells. These are called induced pluripotent stem cells. Why would using these cells in medicine generate fewer ethical issues than using other cell types.

No embryos need to be created and then destroyed to obtain these stem cells as they are produced from differentiated adult cells which are originally found in several types of tissues.

What are the advantages of asexual reproduction

Not needing to spend time and energy seeking a receptive mate large number of offspring can be produced quickly and efficiently All offspring are genetically identical allowing them to be well adapted to a favourable environment. No relying on a vector (plants)

Splitting in single celled eukaryotes

Not the same as binary fission Cell splitting in eukaryotes happened by mitosis- cell splitting in a single celled organism is really cytokinesis (difference between cytokinesis in humans and in a single celled organism is that at the end of cytokinesis in a single celled organism, the cell will have divided into two and produced two separate organisms)

Parthenogenesis

Only occurs in some animal species (very rare) Females produce eggs, and the egg develops into a new organism without being fertilised by a male therefore the offspring are always female

Pluripotent stem cells

Pluripotent stem cells can give rise to all the cell types that make up the body but not all cell types that make up the embryonic membranes (eg; placenta and chorion). An example of pluripotent stem cells is the inner cell mass.

Proto-oncogenes

Proto-oncogenes are a special group of normal genes that are involved in the regulation of cell division. Proto-oncogenes stimulate cell growth and are not required for normal growth and development of cells. Mutations of these genes can change them into oncogenes. Oncogenes induce uncontrolled cell division

Inherited genes

Some people have a predisposition to certain forms of cancer inherited from their parents. Examples include breast cancer which is associated with BRCA1 and BRCA2 located on chromosome 17. A protein coded by these genes takes part in the repair of damaged DNA, but changes in its structure can lead to uncontrolled cell growth.

Spore formation

Some plants conserve energy and water by producing spores- Hardy, self-contained capsules that contain the DNA instructions required to produce a new plant in times of rain. Spores are single-celled structures formed by cell division (mitosis) in a parent organism. Spores detach from the parent organism and develop into new individuals in suitable environmental conditions. Fungi reproduce through spores

Explain the importance of stem cells to the body

Stem cells are undifferentiated cells found in multicellular organisms that have the potential to replicate and to develop into many different kinds of cells.

Suggest how stem cells could be potentially useful for treating diseased or damaged organs.

Stem cells can differentiate into many cell types, therefore they have great potential for therapeutic use and tissue replacement which can assist in treating a number of diseases.

Issues with cloning and disadvantages

Success rate is low- hundreds of wasted embryos Dolly lived to half the age of the average sheep- short lifespan, suffer from diseases Objections on ethical and religious backgrounds Disadvantages Expensive Animals cloned with adult somatic cells are going to age more rapidly due to the cells having shorter telomeres ( lived half their lifespan)

Artificial embryo splitting (cloning)

Take egg and sperm from two organisms (eg cow and bull) and fertilise them in a laboratory to produce a zygote. The zygote will divide to create an embryo, and when the embryo has between 8-16 cells, a fine glass instrument is used to divide the nucleus in half resulting in two embryos. These embryos will continue to divide and eventually result in two genetically identical organisms (calves)

Potency of stem cells

The ability to differentiate into specialised cells. There are different levels of potency that depend on the type of stem cell.

Explain why the cross wall is important in binary fission

The cross walk forms across the cell and divides it into two cells of identical genetic composition which is therefore how new cells in most prokaryotes are formed

Budding

The development of a new organism or parts of an organism from an outgrowth of the parent organism. The new organism may detach from the parent and grow to adult size. If the new individual remains to the parent, a branching colony is formed. Sponges and most cnidarians eg Hydra, can reproduce by budding

Fission

The division of a parent nucleus by mitosis and then division of a cytoplasm to produce two new daughter cells. Amoebae are single celled, eukaryotic organisms possessing a nucleus and other membrane bound organelles that reproduce by binary fission.

Zygote

The first cell of a new individual formed by the fusion of a sperm and an ovum at fertilisation

Explain why sexual reproduction might be advantageous to a species living in a changeable environment.

The greatest advantage of sexual reproduction is that offspring all vary from one another and from their parents. In a changing environment, there is a greater chance that some of the offspring carry genetic combinations that make them better suited to the new conditions and therefore better able to survive and reproduce.

Explain the term generation time

The time required for a bacterial cell to divide or for a population of bacterial cells to double is called the generation time

Chemical carcinogens

Tobacco- contains mutagens and carcinogenic compounds Air pollution- factories can emit smoke containing chemicals that increase risk of developing cancer

Totipotent stem cells

Totipotent stem cells can give rise to all the cell types that make up the human body and all the cell types that make up the membranes that surround the developing embryo (including the placenta). For example in humans, the zygote and its first few divisions, and the tissue at the root and shoot tips of plants is also totipotent.

Tumour suppressor genes

Tumour suppressor genes are a group of genes that code for proteins involved in slowing down cell division, the repair of DNA or apoptosis. If these genes are damaged cell division may be unchecked.

Vegetative reproduction

Vegetative propagation involves part of a plant body becoming detached and developing into a new individual. Vegetative propagation can be performed artificially and one technique is known as grafting. With this method, the cut stem of one plant is attached to the stem and roots of another. This method of propagation is commercially important to growers of fruit trees and roses as it enables the reliable production of plants with desirable qualities. The runners produced in strawberry plants are an example of vegetative propagation.

Biological

Viruses such as HTLV-1, human papilloma virus, hepatitis B and Epstein Barr virus

List three events in which chromosomes can influence variation in offspring

When homologous chromosomes separate and recombine in the first division of meiosis, pieces of chromosomes sometimes break and exchange with their homogenous pairs during crossing over. This can lead to variations in the appearances of the offspring. The process of fertilisation also provides the potential for different combinations of characteristics in the offspring because it is by chance that particular gametes combine.

Physical carcinogens

X-rays and nuclear radiation Over exposure to sunlight or tanning beds- increasing risk of skin cancer or melanoma

a male zebra and female donkey mated to produce a hybrid animal called a zonkey. the diploid number of the donkey, Equus asinus is 62 and the diploid number of the zebra, Equus quagga is 44 a- how many chromosomes would be present in the egg of the donkey? b- name the type of cell division involved in the formation of the egg of the donkey? c- how many chromosomes would be present in the somatic tissue of a true zonkey? d- explain how you worked out the chromosome number you have given as an answer in the previous question? e- explain why there would be problems with gamete formation in a zonkey?

a- 31 (half of 62) b- meiosis c- 53 d- 62/2 = 31 + 44/2= 22 = 53 e- No homologous chromosomes

During mitosis... a- the spindle forms during prophase b- chromatids separate to opposite poles of the spindle during metaphase c- homologous chromosomes separate to opposite poles of the spindle during anaphase d- homologous chromosomes line up at the equator of the cell during telophase

a- the spindle forms during prophase

when comparing normal meiosis in human males and females: a-equal numbers of functional gametes are formed from each participating cell b- each egg and sperm contain a single sex chromosome c- each egg produced contains one more autosome than a sperm cell d- all sperm contain the same kind and amount of DNA

b- each egg and sperm contain a single sex chromosome

as a result of mitosis in an animal cell, each of the daughter cells which are formed: a- have twice the number of chromosomes as the parent cells b- have half the number of chromosomes as the parent cells c- have no chromosomes until the first mitotic division d- have the same number of chromosomes as the parent cells

d- have the same number of chromosomes as the parent cells

What are the disadvantages of asexual reproduction

having very little genetic variation which leaves the population susceptible to infection and environmental changes. Whole communities of genetically identical individuals may not survive these changes. As a large number of offspring are produced, there may be increased competition for limited resources if the offspring are close together.