B5. How do organisms develop? How are multicellular organisms different to single celled organisms? Cells in multicellular organisms are specialised to

B5

How do organisms develop?• How are multicellular organisms different to

single celled organisms?• Cells in multicellular organisms are specialised

to do particular jobs• Groups of specialised cells are called....• Tissues• Groups of tissues form.......• Organs

How do organisms develop?• What is a fertilised egg cell called?• Zygote• By what process does the zygote divide?• Mitosis• What does the dividing zygote form?• Embryo • What are the cells called at the embryonic stage?• Embryonic stem cells• What is unique about these cells?• Identical and unspecialised, can develop into any type of cell required by the

organism• What happens after the 8 cell stage?• Most of the embryo cells become specialised and form different types of what?• Tissue

How do organisms develop?

• What happens to some of the adult cells as the foetus develops?

• Remain unspecialised (adult stem cells) and can become specialised at a later stage

• What is a limitation with adult stem cells?• Can only develop into a limited number of

cell types

How do organisms develop? - Plants

• What are the regions in a plant called where cells are mitotically active?

• Meristems• What does “mitotically active” mean?• Cells can divide by mitosis• What are meristem cells?• Unspecialised plant stem cells• What do meristem cells and embryonic stem cells have

in common?• Both can specialise into ANY cell type


• What type of tissue can meristem cells turn into?• Any – xylem, phloem, flowers, stem, leaves,

roots• Why does the presence of meristem cells make

cloning plants easy?• Plant tips contain meristem cells and so you can

cut a tip and re-grow the cutting as it will contain meristem cells that can produce any tissue type


• What do we call the cuttings from the parent plant?

• Clones• Why is the process of taking cuttings an

advantage for farmers?• Grow plants quickly with DESIRABLE

FEATURES


• What hormone can promote the growth of roots on a cutting?• Auxin• Explain PHOTOTROPISM• Growth towards light• When directional light falls on a plant stem• Meristem cells in the tip will allow growth• Auxins in the tip will diffuse to the darker side of the stem• Diffuse along the darker side• Auxin promote rapid cell growth along the darker side• Stem grows quicker along the darker side• Stem grows/bends towards the light


• Why is phototropism so important to a plant?• Ensures a plant’s survival as it maximises the

amount of sunlight the plant absorbs for photosynthesis – increases growth

• Auxin diffuses away from the light

How does an organism produce new cells?

• Mitosis:• What type of cell is produced from mitosis?• Cells that are genetically identical to the parent

cell• What two things occur during cell growth?• Number of organelles (structures in cells e.g.

Mitochondria) increase• Chromosomes are copied – two strands of DNA

separate and new strands form alongside them


• What two things occur during mitosis?• Copies of the chromosomes separate• Nucleus divides• What type of cell is produced from meiosis?• Cells that are gametes – have half the chromosomes of

the parent cell and so are not genetically identical• Explain how a zygote obtains a full set of chromosomes• The zygote has a full set of chromosomes as the zygote

has chromosomes from each parent (from each gamete)


• Why does an organism produce new cells?• Growth and repair• Meiosis is a type of cell division that takes place in humans. • Use ideas about chromosomes to describe how cells made

by meiosis are different from cells made by mitosis, and why this is important

• Cells made by meiosis contain half the number of chromosomes of the parent cell but cells made by mitosis have the same number of chromosomes.

• This is important because meiosis produces gametes, which fuse with other gametes during fertilisation to make a cell/zygote with the correct number of chromosomes

How do genes control growth and development within the cell?

• What structure does the DNA molecule have?• Double helix• What are the four DNA bases and how do they pair up?• A with T• G with C• Why is the order of the DNA bases so important?• Genetic code for the production of a protein (contains

instructions for producing proteins)• Where is the genetic code in a cell?• Nucleus


• What is a gene?• Section of DNA that contains the instructions to produce a

particular protein in a cell• What is an amino acid?• Chemical unit that makes up a protein• How many different amino acids are there?• 20• How are there so many different proteins produced in a cell?• The specific order of the amino acids produces different

proteins• Where are proteins made in the cell?• Cytoplasm


• Explain how the order of bases in a gene produces a specific sequence of amino acids to make a particular protein

• Every three bases is called a triplet• Each triplet codes for a specific amino acid• So the order of the bases decides which amino acid is

produced• The order of the triplets decides the order of the

amino acids• Called triplet code


• How does the triplet code in the nucleus produce a protein in the cytoplasm?

• Two DNA strands unzip • A copy of the gene is made as a molecule of mRNA• Molecule of messenger RNA (mRNA) is made using one strand of

the DNA as a template• mRNA molecule is smaller than the DNA molecule so can move

out of the nucleus through the nuclear membrane• Joins onto a ribosome in the cytoplasm• The ribosome joins amino acids together, in the order shown on

the mRNA molecule• This amino acid chain forms a protein


• Why aren’t the same proteins produced in ALL cells?

• Genes are switched off in certain cells. The cells produces only the specific proteins they need

• Only the genes that are needed for the cell to function are switched on

• What is unique about embryonic stem cells?• Any gene can be switched on during development

to produce any type of specialised cell


• How can these stem cells be useful in medicine?

• Can be manipulated to produce cells to replace damaged tissue

• People with blood diseases e.g. Leukaemia can be given bone marrow transplants

• Bone marrow contains adult stem cells that can produce new blood cells to replace cancerous ones


• How can cloning be used to make stem cells?• Take an egg cell and remove the nucleus• Take a body cell from the adult patient and remove the

nucleus• Place the nucleus from the body cell into the empty egg cell• Under the right conditions, inactive genes can be switched

on in the nucleus to form an embryo• Stem cells from the embryo can then be used to form new

tissue• Can switch on inactive genes in the stem cells to form

different tissue types

Documents

B5. How do organisms develop? How are multicellular organisms different to single celled organisms? Cells in multicellular organisms are specialised to