Topic 3B: Mitosis, Meiosis and Reproduction

core practical 6:

use of warmed hydrochloric acid

cold water

stain

squashing

• hcl: soften tissue by dissolving middle lamellae

• warmed: increase cell permeability for stain to enter

• cold water: cool down & stop hcl from destroying cellular structures

• stain: warm (intensifies colour & increase diffusion of stain to cells) acetic orcein (stains chromosomes deep purple)

• squash: flatten and disperse cells for easier observation

head of sperm

acrosome: contains enzymes that digest zone pellucida and follicle cells

nucleus: highly condensed haploid chromosomes

middle piece of sperm

abundant mitochondria to release energy by respiration for swimming to ovum

tail of sperm

flagellum: for movement

large cytoplasm of ovum

food reserve

zona pellucida

with glycoprotein receptors to bind with sperms

cortical granule

fuse with zona pellucida is to release enzymes that destroy sperm binding sites & thicken and harden jelly of zona pellucida to form tough layer that prevents polyspermy

mechanism of mammalian fertilisation

1. the front of a sperm touches the zona pellucida of the oocyte and acrosome reaction is triggered

2. digestive enzymes pour out of the opened acrosome and begin to digest the zona pellucida and follicle cells

3. membrane of sperm head fuse with oocyte membrane and cortical reaction is triggered

4. cortical granules fuse with zona pellucida and releases enzymes into the zona pellucida, which destroy sperm-binding sites, & thicken and harden the jelly of the zona pellucida to form a tough fertilisation membrane that prevents polyspermy

mechanism of plant fertilisation

1. pollen falls onto stigma

2. pollen tube grows from pollen tube cell nuclei to style

3. generative cell divides to form 2 male gamete nuclei

4. 1 haploid male nucleus fused with the female gamete to form diploid zygote

5. another haploid male nucleus fuses with 2 polar nuclei to form triploid endosperm nucleus