B5 - Growth and Development

B5 - Growth and Development

1. Specialized Cells

   • Cells with features that enable it to carry out specific functions e.g. neurons

2. Tissue

   • A group of specialized cells that carry out a function e.g. nervous tissue

3. Organ

   • A group of tissues that carry out a function e.g. Brain

4. Organ System

   • A group of Organs that carry out a specific function e.g. Nervous System

5. Zygote (fertilised egg)

   • Cells divided by Mitosis to produce an Embryo
     • After about 2 months, when the main organs are fromed, it is referred to as a foetus
       • At this stage, cells start to become specialized

6. Growth

   • Animal Growth
     • As an Animal grows larger, all of its organs also grow larger, so growth must occur throughout the whole body. Eventually growth will stop, but cells will continue to grow and divide as cells are also dying. Due to the rate of growth and death generally being the same there is no more growth.
   • Plant Growth
     • Although plants get larger overall, they only actually grow at specific places called Meristem regions which is where mitotically active cells (actively dividing cells) called Meristem cells are found.
       • Meristem Cells are unspecialized cells that are found at shoot tips, root tips, in buds and in the stem.

7. Cloning Plants

   • Rooting powder contains growth hormones, which stimulates the meristem cells to divide and then roots grow from the cut portion of the stem.

8. Phototropism

   • The response of a plant to a light source
     • Plant shoots always grow towards sunlight
   • If light is multilateral, or right above the shoot, the plant grows straight up and Auxin is evenly distributed.
   • If sunlight is on one side of a plant, Auxin will diffuse to the shady side of the shoot and will cause these cells to elongate so that the shoot can move towards the sunlight
     • Auxin is a plant growth hormone that stimulates cells to elongate

9. DNA

   • Adenine + Thymine
     • Cytosine + Guanine
   • DNA is in the Nucleus of the cells
     • DNA is a double Helix
       • DNA is long stringy and can be pulled into long strings unlike Proteins
   • mRNA is shorter and thinner than DNA and Thymine is replaced with Uracil
     • mRNA is a single stranded copy of DNA which joins with a Ribosome which reads the genetic code in the mRNA and assembles the proteins needed
   • DeoxyriboNucleicAcid
   • Scientists found out which letters out of A, T, C and G matched with which because they saw that there were the same amounts of A's and T's and C's and G's however they saw that there were different numbers of C's and A's and so on
   • DNA Replication
     • Double Helix unwinds
       • DNA strands are separated by Enzymes
         • Freebases on the DNA strands pair up with free complementary bases in the Nucleus
           • Two new DNA strands wind back up

10. Proteins are made of Amino Acids

    • Proteins are made in the Cytoplasm

11. Protein Synthesis

    • Section of DNA Helix that codes for one protein unwinds
      • DNA acts as a template for a strand of mRNA (T is replaced with U) (This is called Transcription)
        • mRNA leaves the Nucleus through a nuclear pore
          • mRNA attaches to a Ribosome in the Cytoplasm
            • tRNA molecules attach to a sequence of three bases on the mRNA strand (triplet code) and deliver an
              • Amino Acids are attached together in a chain at the Ribosome. The order of Amino Acids is determined by the mRNA sequence. The chain of Amino Acids is a Protein. (This is called Translation)

12. Mitosis

    • Chromosomes become visible and Nuclear membrane starts to disintergrate
      • Nuclear membrane fully breaks down and chromosome pairs line up in the centre of the cell
        • chromosomes are pulled apart by spindle fibres to opposite sides of the cell
          • New Nuclear membranes form around each set of chromosomes
            • The cell membrane splits, forming two genetically identical cells
    • If Mitosis goes wrong, Cancer can be caused as there is uncontrolled cell growth

13. Meiosis

    • DNA of each chromosome is replicated, producing twice the number of chromosomes
      • Nuclear membrane disintegrates then chromosomes line up in the centre of the cell
        • Chromosomes are pulled apart by spindle fibres then new nuclear membranes form and cells divide
          • Nuclear membranes break down and chromosomes line up in the centre of the cell
            • Chromosomes are pulled apart again. New membranes form around chromosomes. cells divide again

14. Gene Switching

    • One gene codes for one type of protein. as human cells have about 30,000 genes, an embryonic stem cell can make 30,000 types of protein molecules
      • In early Embryos all cells are unspecialized, all the genes in their DNA are switched on and they produce thousands of proteins. As these embryonic stem cells differentiate to form specialized cell, some genes are switched off by 'junk DNA' which control genes. This means cells now only produce the proteins they need to perform their function.

15. Stem Cells

    • Uses
      • Therapeutic Cloning
      • Growing new Tissues
      • Growing new Organs
    • Where are they found?
      • Umbilical Cord Blood
      • Embryos
      • Adult Stem Cells are found in Tissues

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