Explain the ACROSOME REACTION.
- 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
Explain the process of PLANT 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)
What are the uses of MITOSIS?
- growth of multicellular organisms
- repairing damaged tissues
- some organisms: important for reproducing asexually producing offspring that is genetically identical to parent offspring
Describe the CORE PRACTICAL on how to observe MITO
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.
Define STEM CELLS.
- undifferentiated/ unspecialised cells
- which can keep dividing
- and give rise to other types of cell
Describe the different stages of Mitosis.
- INTERPHASE: G1 phase/ S phase (DNA replication)/ G2 phase
- so the cell has enough organelles, DNA and cytoplasm for 2 new cells
- chromosomes shorten and thicken
- centrioles move to opposite ends, forming spindle across cell between 2 poles
- nuclear envelope breakdown (nucleolus disappears)
- chromosomes' centromeres attach to spindle fibres at the equator
- spindle fibres contract, pulling chromosomes apart - one chromatid of each chromosome is pulled to each pole of the spindle
- spindle breaks down
- chromosomes unravel
- nuclear envelope reforms around 2 groups of chromosomes
- nucelolus reappears
- CYTOPLASMIC DIVISION
- cytoplasm divides
- 2 identical daughter cells are produced
How would you demonstrate TOTIPOTENCY by PLANT TIS
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.
- same batch agar
- same light level
- same temperature
Describe how DIFFERENTIATIONAL GENE EXPRESSION res
- 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
How can the transcription of genes be prevented?
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
Describe 3 differences between Eukaryotes and Prok
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)
How could DNA damage in the embryo result in inher
- 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
Explain the importance of fertilisation in sexual
- restores the diploid number of chromosomes
- combines the genome from 2 cells, which is important for GENETIC VARIATION
What is the function of the GOLGI APPARATUS, SMOOT
- modifies and packages lipids and proteins in vesicles for transport
- makes lysosomes
- makes lipids and steroids
- site of protein synthesis
Explain the TRANSPORT of PROTEINS within the cell
- ribosome on rough endoplasmic reticulum
- golgi apparatus
- cell surface membrane
- out of cell by EXOCYTOSIS