1. B5 Growth and Development
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B5 Growth and Development
OCR 21st Century
W Richards
The Weald School

2. B5.1 How do organisms develop?
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B5.1 How do organisms develop?

3. Cell specialisation
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During the development of a multi-celled organism cells differentiate to form specialised cells:
White blood cell
Egg cell (ovum)
Ciliated epithelial cell
Nerve cell (neurone)

4. Cells, tissues, organs and systems
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Basically, all living things are made up of cells…
A group of CELLS makes up a TISSUE
A group of TISSUES makes up an ORGAN
A group of ORGANS makes up a SYSTEM
A group of SYSTEMS make up an ORGANISM

5. Here’s another example in humans:
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Here’s another example in humans:
Muscle cells
Muscle tissue
Organ
System
Organism

6. Fertilisation
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The human egg and sperm cell (“GAMETES”) contain 23 chromosomes each and are created by meiosis.
When fertilisation happens the gametes fuse together to make a single cell called a ZYGOTE. The zygote has 46 chromosomes (23 pairs) and continues to grow through mitosis.

7. Embryos
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When the zygote grows all of the initial cells are identical (up to the 8-cell stage). These are called “embryonic stem cells”. From this stage on the cells grow through mitosis and start to specialise.

8. Adult Stem Cells
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It is also possible to have adult stem cells – these are unspecialised cells that can become specialised later (but they can’t form ALL types of cell)
Adult stem cells can be found in places like bone marrow.
White blood cell
Egg cell (ovum)
Ciliated epithelial cell
Nerve cell (neurone)

9. Plant Growth Introduction
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Plants grow due to their cells dividing through mitosis. The cells then specialise into root hair cells, palisade cells etc. Unlike animals, plants continue to grow for the rest of their lives.

10. Plant Growth - Meristems
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Plant growth occurs in areas called meristems. These meristems are “mitotically active”:
This meristem causes the plant to grow upwards.
This meristem causes the plant to grow in width.
Cells from the meristem behave like stem cells – they can develop into any kind of cell. Cloned plants can be produced from these cells.

11. Cloning Plants by tissue culture
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1) Scrape of a few cells from the desired plant
2) Place the scrapings in hormones (“auxin”) and nutrients
3) 2 weeks later you should have lots of genetically identical plants

12. Plant Hormones
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The growth of roots and shoots is controlled by hormones:
In the shoots the hormone auxin is “destroyed” by light, so the shoot will bend towards the light as the cells on the shaded side grow quickest.
In the roots hormones slow down growth of the cells in the lower region, which makes the root bend down.

13. Some Definitions
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Shoots grow towards light (positive phototropism) and against gravity (negative geotropism).
Roots grow away from light (negative phototropism) and in the direction of gravity (positive geotropism).

14. B5.2 How does an organism produce new cells?
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B5.2 How does an organism produce new cells?

15. Cell growth 1 - Mitosis The chromosomes are copied…
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The chromosomes are copied…
Each daughter cell has the same number of chromosomes and genetic information as the parent – it’s a “clone”.
The chromosomes separate…
The nucleus divides…

16. Each daughter cell has half the number of chromosomes of the parent.
Cell growth 2 - Meiosis
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Each daughter cell has half the number of chromosomes of the parent.

17. Mitosis vs. Meiosis Mitosis: Meiosis:
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Mitosis:
Used for growth and repair of cells
Used in asexual reproduction
Cells with identical number of chromosomes and genetic information are produced (“clones”)
Meiosis:
Used to produce haploid gametes for sexual reproduction
Each daughter cell has half the number of chromosomes of the parent
During meiosis copies of the genetic information are made and then the cell divides twice to form four daughter cells.

18. Fertilisation Revision
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The human egg and sperm cell (“GAMETES”) contain 23 chromosomes each and are created by meiosis.
When fertilisation happens the gametes fuse together to make a single cell called a ZYGOTE. The zygote has 46 chromosomes (23 pairs) and continues to grow through mitosis.

19. B5.3 How do Genes control growth?
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B5.3 How do Genes control growth?

20. Genes, Chromosomes and DNA
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21. Words – helix, amino, code, bases, proteins
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How genes work - DNA
Some facts:
- DNA has a “double ______” structure
- This contains instructions on what a cell does, how the organism should work etc
- The instructions are in the form of a ______
- The code is made up from the four ____ that hold the strands together with hydrogen bonds; A always pairs with T and C with G
- The bases represent the order in which _____ acids are assembled to make specific ________
Words – helix, amino, code, bases, proteins

22. Making proteins 1) DNA “unravels” and a copy of one strand is made
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1) DNA “unravels” and a copy of one strand is made
2) The strand copy is made to produce RNA
3) The copy (with its code) then moves towards the ribosome
4) The ribosome “decodes” the code which tells the ribosome how to make the protein
In other words, genes do NOT leave the nucleus but a copy of the gene (the mRNA) carries the genetic code to the cytoplasm.

23. Adult Stem Cells
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Cells inside an organism contain the same genes. So how can cells specialise if they have the same genes and make the same proteins?
The reason is that many of the genes in the nucleus are “switched off” so that the cell only produces the proteins it needs.
It is possible to “switch on” different genes to make the cell produce different proteins – this is the basis of stem cell research.

24. Should these embryos be treated as humans?
Stem cell research
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As well as adult stem cells from bone marrow, stem cells can also come from...
These stem cells have the potential to develop into any kind of cell. The rest of the embryo is destroyed. Most of these embryos come from unused IVF treatments.
Embryo
Egg and sperm
Cloned embryos
The ethical issue:
Should these embryos be treated as humans?

25. Cloning Animals Here’s how Dolly the sheep was cloned:
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Here’s how Dolly the sheep was cloned:
Host mothers
Clone
It is possible to “switch on” inactive genes in the nucleus of a body cell to form cells of all tissue types. Are cloning and stem cell research the way forward???