test 3 (sex cells and shit)

• cell division • for growth and repair • in somatic cells • a continuous process

• G1 (first growth phase) new proteins produced, grows and carries out normal tasks • S phase (synthesis phase), DNA duplicates • G2 (second growth phase), preparation for cell division • M phase (mitotic phase), cell divides into 2 daughter cells

-G1-S phase dna forms copies of itself during the S phase

• 2 pairs of centrioles become visible early on • centrioles move to piles • centrioles begin to produce spindle (microtubules) • nuclear membrane breaks down • chromatin tightly coils and chromosomes become visible • chromosomes are made of two chromatids joined at centromere

• chromosomes line up down equator of cell - centromere attached to a spindle fibre

• chromosomes seperate at centromere • chromatids pulled by spindle fibres to poles of cell • move away from equator to poles

• chromosomes form tight groups at each pole • nuclear membrane forms • nucleolus appears • spindle fibres disappear • the cell is pinched into two daughter cells

• division of the cytoplasm • furrow develops between the two nuclei • furrow deepens and cuts cytoplasm in half, results in two daughter cells

• parent cell divides twice • four daughter cells are produced in meiosis (2 in mitosis) • chromosome number is haploid (diploid crops divide to become haploid cells) • the daughter cells are not genetically identical • only occurs in sperm and ova

• in mitosis, the centromere divide so that each chromatid becomes a chromosome • in meiosis, the chromatids are not split apart, instead the whole chromosome moves

• there is no interphase 2 in meiosis - dan does not double in preparation for the second division

• chromosomes condense and become visible - spindle fibres start to form

-chromosomes line up down equator and spindle fibres attach

-chromosomes are split at the centromere and sister chromatids are pulled to opposite poles

• spindles disappear • nuclear membrane forms • cytokinesis - cytoplasm is split • 4 non-identical daughter haploid cells

• all stages occur in testes continuously after puberty • spermatogonia begin dividing by mitosis • daughter cells grow and become primary spermatocytes • final stage occurs when the spermatic matures into spermatozoa • takes 72 days

• microscopic • tail is used to propel cell forwards • the head contains nuclear material and enzymes • the middle has mitochondria

• millions of egg mother cells (oogonia) develop before birth in the ovaries • these cells divide by mitosis and will become ova • oogonia grow into primary oocytes • at birth, ovum is still in prophase 1 • 1 per month matures metaphase 2 • meiosis is complete if fertilised • produces 1 viable ovum and up to 3 polar bodies

• two testes • site of spermatogenesis • works best at 35°C • testes can contract/ expand depending on weather

• lobules filled with tiny tubes • tubules lined with cells that produce sperm • interstitial cells lay in between the seminiferous tubules— produce testosterone • larger tubes join to form ducts • ducts lead out of testes via epididymus —> vas deferens

-sperm stored here for up to a month

-carries speed away from testes and connects to urethra

-require: a water medium to swim a nourishing environment that provides sugars they need to fuel their journey protection against acidic conditions of vagina

• made up of a connective tissue (stroma- made up of a layer of germ cells) • endocrine glands secrete oestrogen and progesterone