B5 - Growth and Development Flashcards
What are living organisms made up of?
Cells
Give 2 examples of multicellular organisms
- Humans
- Plants
What do similar cells form?
A tissue
What do groups of tissues form?
And organ
What do groups of organs form?
They make up systems within the whole organism
By which 2 processes do cells divide?
- Mitosis
- Meiosis
What is mitosis?
The division of body cells to produce new cells
Each new cell from the process of mitosis has what? (3 things)
- Identical sets of chromosomes as the parent cell
- The same number of chromosomes as the parent cell
- The same genes as the parent cell
For what 3 reasons does mitosis occur?
- For growth
- For repair
- To replace old tissues
To enable mitosis to take place, cells go through a cycle of ___a)____ and then ___b)____.
a) growth
b) division
For how long does the cycle of growth and division in the process of mitosis take place?
Until the cell can no longer divide
What 2 things happen when a cell enters the growth phase of the mitosis cycle?
- The number of organelles increase
- The chromosomes are copied (the two strands of each DNA molecule separate and new strands form alongside them)
What 2 things happen when a cell enters the division phase of the mitosis cyle?
- The copies of the chromosomes separate
- The cell divides
Explain the process of mitosis.
1) Parent cell with two pairs of chromosomes - each chromosome copies/replicates itself
2) The copies are pulled apart. Cell now divides for the only time in this mitosis sequence
3) Two ‘daughter’ cells are formed
Which places are the only places that mitosis can occur?
In the testes and ovaries
What is meiosis?
A special type of cell division that produces gametes (sex cells) for sexual reproduction
What are gametes?
Sex cells
How many chromosomes do gametes contain compared to their parent cells?
Half the number of chromosomes
Explain the process of meiosis.
1) Cells with two pairs of chromosomes - each chromosome replicates itself
2) Chromosomes part company and move to opposite sides with their ‘copies’
3) Cell divides for the first time
4) Copies now separate and the second cell division take place
5) Four gametes, each with half the number of chromosomes as the parent cell.
Give examples of gametes
Eggs and sperm
What happens during fertilisation?
A male gamete (sperm) and a female gamete (egg) fuse together to produce a single body cell called a zygote
What is the name of the single body cell produced through fertilisation?
A zygote
Because gametes only have half the number of chromosomes as the parent cell, how many chromosomes will the zygote that’s produced contain?
Gametes only have half the number of chromosomes as the parent cell, so the zygote that’s produced has one whole set of chromosomes.
Where does each chromosome come from in a new pair of chromosomes?
One chromosome comes from the father and one chromosome comes from the mother.
Through what process does a zygote divide to produce the cluster of cells called an embryo?
Meiosis
When a zygote divides by meiosis, what is produced?
A cluster of cells = an embryo
What is the name for the cluster of cells produced when a zygote divides by meiosis?
An embryo
Complete:
The embryo continues to divide by ___a)___ (from one cell to two, to four, to eight, etc) after which the cells become ___b)___, until birth as a fully developed ___c)___.
a) mitosis
b) specialised
c) baby
What do meiosis and sexual reproduction produce between offspring and parents?
Variation
How do meiosis and sexual reproduction produce variation between offspring and parents?
- When the gametes fuse, genetic information from two individuals is combined
- For each gene, just one of each parent’s alleles is passed on
- Each offspring can have a different combination of alleles from either parent
- The offspring have different characteristics from each other
Where can genes be found?
In the chromosomes within each cell nucleus
What 2 things can genes control?
- Growth and development in organisms
- The development of characteristics, e.g. eye colour
How do genes control characteristics?
By providing instructions for the production of proteins
In what form do a gene’s instructions for producing proteins come?
In a code made up of four bases (that hold the two strands of the double helix of the DNA molecule together)
How do the 4 bases of genetic code always match up?
Adenine (A) pairs up with Thymine (T), and Cytosine (C) pairs with Guanine (G).
What does the A base in genetic code stand for?
Adenine
What does the T base in genetic code stand for?
Thymine
What does the C base in genetic code stand for?
Cytosine
What does the G base in genetic code stand for?
Guanine
What does Adenine (A) always pair up with in the bases of genetic code?
Thymine (T)
What does Thymine (T) always pair up with in the bases of genetic code?
Adenine (A)
What does Cytosine (C) always pair up with in the bases of genetic code?
Guanine (G)
What does Guanine (G)always pair up with in the bases of genetic code?
Cytosine (C)
What is a gene?
A small section of DNA within the chromosome
The order of the bases in the DNA section is the genetic code for the production of what?
A particular protein
How does a code determine the end characteristics of any organism?
A gene is a small section of DNA within the chromosome. The order of the bases in the DNA section is the genetic code for the production of a particular protein.
True or False?
DNA is able to leave the nucleus.
False - DNA is too large to leave the nucleus
Because DNA is too large to leave the nucleus, what happens to the genes and the production of proteins?
The genes stay inside the nucleus but the production of proteins takes place outside the nucleus (in the cytoplasm)
Where outside the nucleus does the production of proteins take place?
In the cytoplasm
Because the production of proteins takes place outside the nucleus in the cytoplasm, what has to happen to information stored in the genes?
It has to be transferred into the cytoplasm
How is information stored in genes transferred outside the nucleus into the cytoplasm?
- The relevant section of DNA is unzipped
- Instructions are copied onto smaller molecules called mRNA (messenger RNA) [HT]
- These molecules leave the nucleus and carry the instructions to the ribosomes
- The ribosomes follow the instructions to make the relevant protein
The sequence of bases in a gene determines the order in which ___a)___ are joined together to make a particular ___b)___. (HT)
a) amino acids
b) protein
What is the name for the codes for one amino acid in a protein chain, created from a group of 3 base pairs? (HT)
Triplet code
How many different amino acids can be created through the triplet code? (HT)
20
True or False?
The structure of the protein depends on the amino acids that make it up. (HT)
True.
Explain the process by which triplet codes are used to create amino acids. (HT)
- DNA unravels at the correct gene
- A copy of the coding strand is made to produce mRNA
- The mRNA copy moves from the nucleus into the cytoplasm
- The triplet code is decoded by the ribosomes
- Amino acids are joined together to form a polypeptide (protein)
How can a triplet code be decoded? (HT)
By the ribosomes
What are amino acids joined together to form? (HT)
A protein called polypeptide
Up to the 8 cell stage, all cells in a human embryo are what? (2 things)
- Unspecialised
- Have any gene switched on to form any kind of specialised cell
Before the 8 cell stage, what are human embryos called?
embryonic stem cells
Once a human embryo reaches the 8 cell stage, what 2 things do the cells become?
- Specialised
- Form different types of tissue
The cells contain the same __a)___, but many are not ___b)___ (switched off) because the cell only produces the ___c)___ it needs to carry out its role.
d) What about specialised cells?
a) genes
b) active
c) proteins
d) In specialised cells, only the genes needed for the cell to function are active (switched on) as it only requires specific proteins (mainly enzymes).
What could stem cells potentially be used to do?
- Help treat diseases and disorders
- Repair damage to various tissues
What are the 3 sources of stem cells?
- Embryos
- Blood from umbilical cord
- Adult stem cells
Only the __________________ are completely unspecialised and can be used to form any cell type.
embryonic stem cells
What needs to be thought about when using embryonic stem cells?
Ethical decisions - this work is subject to government regulation
Explain the process of therapeutic cloning. (HT)
- The nucleus is removed from an egg cell and replaced with a nucleus from one of the patient’s cells
- The egg cell is then stimulated so that it starts to divide (as if it were a zygote)
- At the 8 cell stage, cells can be removed as they’re still unspecialised
True or False?
Adult stem cells will only produce cells of a certain type. (HT)
True.
Adult stem cells will only produce cells of a certain type. Give an example of this. (HT)
Cells for creating blood cells in bone marrow have to be encouraged to grow more of that type of cell by reactivating (switching back on) inactive genes in the nuclei.
What is an advantage of using adult cells for growing replacement tissue? (HT)
They can be taken from the patient, so the patient’s immune system will not reject the transplant
Where can replacement tissue be grown? (HT)
In a laboratory
What is sometimes used to maintain a blood supply during growth of a replacement tissue in a lab? (HT)
A ‘host animal’ (e.g. a mouse)
What are ‘host animals’ sometimes used for? (HT)
To maintain a blood supply during growth of a replacement tissue in a lab
Through what process do plant cells divide?
Mitosis
New cells in plants specialise into the cells of what 3 things?
- Roots
- Leaves
- Flowers
Unlike animals, how can plants continue to grow throughout their lives?
In height and in width
In what area of a plant can plant growth only occur?
In areas called meristems
What are meristems?
Sites where unspecialised cells are dividing by mitosis
Unspecialised cells that are dividing by mitosis in a meristem then:
- Differentiate
- Become specialised
What are the two types of meristem? Explain what the function of each one is.
- Lateral (which leads to increased girth)
- Apical (which leads to increased height and longer roots)
Some plants cells remain unspecialised and can…
…develop into any type of cell.
Cells that remain unspecialised (meaning they can develop into any type of cell) allow clones of plants with desirable features to be produced from what?
Cuttings
If the hormonal conditions in their environment are changed, the unspecialised plant cells can develop into other what?
- Tissues (e.g. xylem and ploem)
- Organs (e.g. leaves, roots, flowers)
What are xylem tubes used by a plant for?
- To transport water and soluble mineral salts from the roots to the stem and leaves
- To replace water lost during transpiration and photosynthesis
What are phloem tubes used by a plant for?
To transport dissolved food to the whole plant for respiration or storage
Plants can be reproduced in what way? (3 stages)
- Cuttings are taken from a plant
- The cuttings are put in a rooting hormone
- Roots start to form and the new plants develop
The new plants are ______________ to the parent plant - they are clones.
genetically identical
What are auxins? (HT)
The main plant hormones used in horticulture, which:
- affect cell division at the tip of a shoot
- cause cells to grow in size just under the tip so that the stem or roots grow longer
How do plants respond to light?
By changing the direction in which they grow.
What is the process called when plants respond to light by changing the direction in which they grow?
Phototropism.
Why do plants grow towards a light source?
Because they need light to survive
Where are auxins produced? (HT)
At the shoot tip
What happens when an auxin moves down the shoot? (HT)
It causes other cells further down the shoot to grow
When light shines on a shoot, what happen to auxin near that source of light? (HT)
Auxin near the light source is slowly destroyed, so there’s more auxin on the far away side from the light. This causes these cells to lengthen faster than those near the light, so the shoot bends towards the light.
What happens when a light source is directly overhead a plant? (HT)
- Auxin is evenly spread through the shoot
- The shoot grows straight up
What happens when a light source is at an angle towards a plant? (HT)
- Auxin is destroyed nearest to the light source
- The auxin is concentrated on the side furthest away from the light
- The shoot bends towards the light
What happens when the tip of a shoot is removed or covered in opaque material? (HT)
The plant will continue to grow upwards as if the light source isn’t there
What happens when the tip of a shoot is covered with a transparent cap? (HT)
It will still grow towards a light source.
What happens when the tip of a shoot is covered with an opaque cylinder is wrapped around the stem, leaving the tip exposed? (HT)
It will still grow towards a light source.
What is the name of the process when plants grow towards light? (HT)
Phototropism
Jonah planted a seedling (a young plant) into a flowerpot and placed it in a greenhouse. His sister moved it so that the Sun only shone on it from one side.
Explain how the seedling would grow and why this would help it to survive.
The Sun shining on the plant from only one side would mean that it would grow towards the light. This is because the growth rate on the dark side is much faster than the light side. This pattern of growth is called phototropism and is caused by hormones. It helps the plant to obtain more sunlight energy for photosynthesis. This allows the plant to produce more glucose, giving it more energy for growth and reproduction, and helping it to survive.
What are the characteristics of stem cells?
They’re unspecialised and can turn into any kind of cell
Why can’t stem cells be taken after the 8 cell stage?
The cells will have become specialised
Why are embryonic stem cells sometimes better to use than adult stem cells?
Embryonic stem cells can develop into any specialised cell, whereas adult stem cells can only develop into some specialised cells
