Topic 3 SNAB Biology

• the sperm reaches the ovum
• cells surrounding the ovum release chemicals, triggering the acrosome reaction
• the acrosome swells and fuses with the sperm cell surface membrane
• digestive enzymes in the acrosome are released
• the enzymes digest through the follicle cells and zona pellucida surrounding the ovum
• the sperm fuses with its cell surface membrane
• the sperm nucleus enters the ovum
• enzymes released from the lysosomes cause the zona pellucida to thicken, preventing the entry of other sperm
• nuclei of the ovum and sperm fuse: fertilisation

• pollen frain germinates on style
• a pollen tube grows down style towards ovary (growth controlled by tube nucleus)
• pollen grain contains 2 nuclei:
  • tube nucleus
  • generative nucleus
• on germination of pollen, generative nucleus divides by mitosis to form 2 halpoid male gamete nuclei
• 2 male haploid gamete nuclei move down pollen tube
• pollen tube grows through small pore (micropyle) into embryo sac
• both male haploid male gamete nuclei enter the embryo sac
• DOUBLE FERTILISATION:
  • 1 of the male gamete nuclei fuses with the egg nuclei --> forms dipliod zygote (divides to form the embryo)
  • 1 of the male gamete nuclei fuses with the 2 polar nuclei in the embryo sac, --> forms triploid zygote (divides to form the seed's storage tissue = endosperm)

- growth of multicellular organisms

- repairing damaged tissues

- some organisms: important for reproducing asexually producing offspring that is genetically identical to parent offspring

1. Cut 5mm onion root tip.

2. Place on watch glass.

3. Add a few drops of HCl.

4. Add a few drops of the stain: ACETIC ORSEIN.

5. Heat by passing over a bunsen burner flame.

6. Put root tip on slide.

7. Place cover slip on top and squah down gently.

8. Observe under microscope.

• undifferentiated/ unspecialised cells
• which can keep dividing
• and give rise to other types of cell

• INTERPHASE: G1 phase/ S phase (DNA replication)/ G2 phase
  • so the cell has enough organelles, DNA and cytoplasm for 2 new cells
• PROPHASE:
  • chromosomes shorten and thicken
  • centrioles move to opposite ends, forming spindle across cell between 2 poles
  • nuclear envelope breakdown (nucleolus disappears)
• METAPHASE:
  • chromosomes' centromeres attach to spindle fibres at the equator
• ANAPHASE:
  • spindle fibres contract, pulling chromosomes apart - one chromatid of each chromosome is pulled to each pole of the spindle
  • spindle breaks down
• TELOPHASE:
  • chromosomes unravel
  • nuclear envelope reforms around 2 groups of chromosomes
  • nucelolus reappears
• CYTOPLASMIC DIVISION
  • cytoplasm divides
  • 2 identical daughter cells are produced

1. Sterilise surface

2. Take a few plant cells of one type (explant) from a growing area of a plant (e.g. root/ shoot)

3. Place the cells on a sterile agar medium with nutrients and growth regulators.

4. Cover with tin foil.

5. Let the plant cells grow and divide by mitosis. Mitosis is shown as: unspecialised cells differentiate into specialised cells that grow and differentiate into an entire plant.

Controls:

• same batch agar
• same light level
• same temperature

• differentiational gene expression is caused by turning different genes on and off, by controlling transciption
• which determines differentiation
• under the right conditions, some genes are activated and some are not
• the active genes make active mRNA
• which is translated into proteins within cell (by ribosomes)
• this controls cell processes and determines cell structure
• --> forming a SPECIALISED CELL

Protein repressor molecules attach to: DNA PROMOTER REGION-

• blocking the attachment site
• preventing the attachment of the TRANSCRIPTION INITIATION COMPLEX

characteristics of an organism, defined by:

• GENOTYPE: genetic make-up
• ENVIRONMENT: in which the individual develops

1. SIZE: Eukaryotes are larger; Prokaryotes are smaller.

2. DNA: Eukaryotes have linear DNA (in nucleus); Prokaryotes have circular DNA (free in cytoplasm)

3. ORGANELLES: Eukaryotes has a nucleus/ membrane-bound organelles such as mitochondria; Prokaryotes has no nucleus or membrane-bound organelles (apart from small ribosomes)

- when the embryo divides by mitosis into an adult

- cells giving rise to testes/ ovaries may have DNA error

- therefore a gamete with faulty DNA can form

- cancer causing error could be passed on in these gametes to next generation

- restores the diploid number of chromosomes

- combines the genome from 2 cells, which is important for GENETIC VARIATION

GOLGI APPARATUS:

• modifies and packages lipids and proteins in vesicles for transport
• makes lysosomes

SMOOTH ER:

• makes lipids and steroids

RIBOSOMES:

• site of protein synthesis

- nucleus

- ribosome on rough endoplasmic reticulum

- vesicle

- golgi apparatus

- vesicle

- cell surface membrane

- out of cell by EXOCYTOSIS