3B Flashcards
what does locus mean
the location of a gene on a chromosome
what are gametes
- they are sex cells in a organism
- they fuse in fertilization to form a zyagote
- they form during meiosis and are haploid cells
how are sperm cells specialised for their function
- have a flagellum tail that allows them to swim towards the egg cell
- contain many mitochondria that allows them to swim
- acrosome that contains digestive enzymes to break down zona pellucida to fertilize the egg cell
how are egg cells specialised for their function
- they are large and most of internal space is nutrients for embryo
- follicle cells that form protactive layer (look like pili)
- have glycoprotein layer known as zona pellucida that forms impenetrable barrier AFTER fertilisation
what does fertilisation mean and what occurs in mammals
- fusion of nuclei from male gamete and female gamete when the head of sperm releases enzymes to digest zona pellucida to create a path for the sperm to pass this is know as acrosome reaction, then egg cell releases vesicles called cortical granules which will causes zona pellucida to harden and thicken this process is known cortical reaction, then the male nuclei fuses with female nuclei to form a zyagote which will divide by mitosis so embryo form
how does fertilisation occur in plants
- after pollination, pollen grain germinate to form pollen tube that reaches the ovary, two haploid male nucleus(generative nucleus) move down the pollen tube
- as generative nucleus travel down pollen tube they divide by mitosis to form two other haploid male nuclei
- double fertilisation occurs where one haploid male nucleus fuses with the nucleus of egg cell to form diploid zygote, the other haploid male nucleus fuses with two polar nuclei in the ovule to form a triploid endosperm nucleus which will form endosperm (food supply for embryo plant)
what are the stages that occur in cell cycle
- interphase
- nuclear division (mitosis)
- cell division (cytokinesis)
- the movment from one phase to another is triggered by cyclins (chemical signal)
what does happen in interphase
- the mass of cell starts to increase in three phases:
- G1: where the cell starts to grown and synthesis protein
- S: replication of DNA
- G2: where the DNA is checked for any errors and and preparations for cell division are made
what does happen in nuclear division (mitosis)
- the process of nuclear division by which two identical daughter nuclei are produced
- mitosis consists of four phases:
- prophase
- metaphase
- anaphase
- telophase
what does happen during prophase
- chromosomes condense and are visible when stained
- centrosomes move to the opposite ends of nucleus
- spindle fibers emerge from centrosomes
- nuclear envelope breaks down to vesicles
what does happen in metaphase
- chromosomes line up at the equator of the spindle
- spindle fibers extend and are attached to the centromeres, each sister chromatid is attached to spindle fiber
what does happen in anaphase
- the sister chromatids are separated and centromere divides into two, spindle fibers shorten and are pulled to the opposite end
what does happen in telophase
- chromosomes begin to decondense
- nuclear envelopes begin reform around each set of chromosomes
- spindle fibers break down
how is mitosis essential for biological processes
The growth of multicellular organisms: daughter cells are identcial to the parent cell, this enables unicellular zygote to grow into mutlicellular organisms
Replacementof cells and repair of tissues: dying cells can be replaced with same cell
asexual reproduction: parent can produce offsprings without need to find a partner
what does happen in cytokinesis
- once nucleus is divided into two identical nuclei, the whole cell divides
- involves constriction of cytoplasm between the tow nuclei and in plant a cell wall forms
