Cell division

Chapter 6

what is the name of a fertilised egg?

zygote

haploid

contains half the normal chromosome number, one chromosome of each type

diploid

contains 2 chromosomes of each type, one from each parent, normal chromosome number

homologous chromosomes

chromosomes found in diploid cells. they have the same genetic information so pair together. they are not identical because they can have different alleles. one is maternal, one is paternal

locus

position on a particular chromosome

what is the significance of mitosis in life cycles?

replacement of cells/repair of tissues. growth. asexual reproduction in plants, animals and fungi

what is the significance of meiosis in life cycles?

produce haploid cells, create genetic variation by crossing over and independent assortment/segregation

what are the names for homologous pairs of chromosomes?

bivalents or tetrads

allele

different versions of the same gene. i.e. eye colour gene. this is known as a gene variant

stages of meiosis

meiosis I - reduction division, 2 haploid daughter nuclei formed. meiosis II - chromatid separate, each haploid cell divides again to form 4 daughter haploid cells

reduction division

number of chromosomes is halved, occurs in meiosis I

centromere

site for spindle fibre attachment, connects the sister chromatids, (each chromosome/chromatid has one that’s why they are both called chromosomes)

Sister chromatids

identical copies of a chromosome that are held together during replication and remain attached until they are separated during mitosis

crossing over

the exchange of genes between homologous chromosomes, resulting in a mixture of parental characteristics in offspring, occurs in prophase, forms chiasma

how can genetic variation occur

Different alleles. Crossing over. Independent assortment and Segregation of chromosomes (metaphase I). Independent assortment and segregation of chromatids (metaphase II). Mutations (can happen in DNA replication/in sperm or egg so then is present in offspring)

Prophase I

chromosomes and centrioles have replicated, nuclear envelope disintegrates, nucleolus disappears, bivalents form, crossing over happens and spindles begin to form

Metaphase I

Homologous chromosomes line up at the metaphase plate in pairs. spindles attach to the centromere of each chromosome, crossing over still occurs

Anaphase I

whole chromosomes are pulled to the poles by spindle fibres - there is no division of the centromere. Chiasma separate sometimes resulting in an exchange of chromatids forming recombinant chromatids causing genetic variation

Telophase I

nuclear membrane reforms, chromosomes begin to uncoil

Cytokinesis I

divides into 2 cells, forms 2 genetically non-identical haploid cells

independent assortment

orientation of homologous chromosomes on the metaphase plate is random and independent of other pairs. maternal/paternal chromosomes can end up facing either pole. occurs during metaphase I, results in different combinations of alleles facing the poles and genetic variation

Independent segregation

when they move to separate cells in anaphase I

Prophase II

chromosomes condense, nuclear membrane disintegrates, spindles form

Metaphase II

individual chromosomes line up on the metaphase plate, spindle fibres attach to their centromere, independent assortment of chromatids (chromatids no longer identical due to crossing over) and genetic variation produced

Anaphase II

centromere divides so each chromatid is now a chromosome. chromosomes are pulled by spindles to poles

Telophase II

chromosomes uncoil, nuclear membrane reforms, nucleolus becomes visible again

Cytokinesis II

4 non-identical haploid cells

Levels of organisation in multicellular organisms

Specialised cells > tissues > organs > organ systems > whole organism

erythrocyte

red blood cell

role of erythrocytes

transport oxygen

adaptations of erythrocytes

no nucleus (increases space available for haemoglobin). contains lot of haemoglobin (to bind to oxygen). biconcave shape (increase SA:V). small and flexible (fit through narrow capillary lumen)

role of neutrophils

part of the immune system

neutrophil

type of white blood cell

adaptations of neutrophils

multi-lobed nucleus (allows movement through fenestrations/gaps to get to the site of infections). granular organisms (contain enzymes in lysosomes that assist in breaking down pathogens)

role of sperm cell

male reproductive cell (gamete)

adaptations of sperm cell

acrosome (digestive enzymes in the head that are released to breakdown the outer layer of the egg cell). flagellum (aid movement). lots of mitochondria (generate a lot of ATP required for movement). haploid nucleus (contains half the required genetic material pre-fertilisation)

role of egg cell

female reproductive cell (gamete)

adaptations of egg cell

haploid nucleus. lots of cytoplasm (contains lots of nutrients to support growth and multiple cell divisions that occur in and around it)

phagocyte

A white blood cell that destroys pathogens by engulfing them and breaking them down

lymphocyte

A type of white blood cell that make antibodies to fight off infections

role of nerve cell

transmits electrical impulses around the body

adaptations of nerve cell

myelin sheath (insulates the axon, speeding up action potentials). lots of dendrites (increase SA to allow for more nerve connections). long thin axon (increases speed of action potentials)

what does action potentials mean?

electrical impulses that send signals around your body

role of palisade cell

main photosynthesis cell

adaptations of palisade cell

lots of chloroplasts (allow a lot of light absorption for photosynthesis). rectangular box shape (cells can pack close together forming a continuous layer to maximise light absorption). large vacuole (maintain turgor pressure). thinner cell wall (allow more light to be transmitted through and increase the rate of diffusion of carbon dioxide). chloroplasts are able to move (greater access to light)

turgor pressure

force within the cell that pushes the plasma membrane against the cell wall. also called hydrostatic pressure

role of root hair cell

maximise absorption of water and mineral ions

adaptations of root hair cell

elongated structure (increases SA:V). vacuole contains a high concentration of solutes (lower water potential inside cell promotes osmosis, net movement of water is in)

role of guard cells

regulates gas exchange and transpiration rate

stomata

Small holes in a leaf that allow gas exchange to occur, stomata = plural, stoma = singular

adaptations of guard cells

inner cell wall is thicker (promotes the opening and closing of the stomata ensuring the do not swell evenly so stomata can open). Allows carbon dioxide in and oxygen out

role of Squamous epithelial cells

found in areas with a flow of liquid (like blood vessels), allow rapid diffusion

adaptations of squamous epithelial cells

thin walls (shortens diffusion distance, allows ease of gas exchange, forms lining of the lungs allowing rapid diffusion of oxygen into the blood). Smooth lining (reduces friction increasing the efficiency of liquid transport)

role of ciliated epithelial cells

keep airways clear of mucus, lines the trachea

adaptations of ciliated epithelial cells

cilia (effective at wafting/beating mucus away from airways), lots of mitochondria (generate ATP required for beating mucus)

what are goblet cells and their purpose?

release mucus to trap any unwanted particles present in the air to prevent them reaching the alveoli in the lungs which may be bacteria

4 main categories of tissues in animals

Nervous - support transmission of electrical impulses. Epithelial - cover body surfaces (internal/external). Muscle - contract. Connective - hold tissues together/ act as a transport medium

2 main categories of tissues in plants

Epidermis - cover plant surfaces. Vascular - transport of water and nutrients

animal specialised cells

erythrocytes, neutrophils, sperm cell, egg cell, nerve cell, squamous epithelial cells, ciliated epithelial cells

plant specialised cells

root hair cell, guard cells, palisade cell

examples of plant tissues

xylem, phloem, (plant epidermis)

examples of animal tissues

cartilage, squamous epithelial cells, ciliated epithelial cells, muscles

cartilage components and roles

elastin (stretch), collagen (strength and structure), chondrocyte (makes other components)

squamous epithelium components and roles

one cell thick (low friction bc smooth)

ciliated epithelium components and roles

goblet cells (secrete mucus), cilia (beat mucus)

muscles components and roles

myofibrils (contraction), connective tissue (growth)

meristem

plant tissue consisting of stem cells. Responsible for the growth of new organs and structures. Apical meristem (found at the tips of roots and shoots). Vascular cambium (between xylem and phloem)

stem cells

renewing source of undifferentiated cells with the potential to differentiate into a variety of specialised cells, can undergo cell division repeatedly

why does speed of cell division need to be controlled

if too slow = aging occurs. if too fast = tumor development

where are erythrocytes and neutrophils produced

stem cells in bone marrow

where are xylem vessels and phloem sieve tubes produced

meristems

3 levels of stem cell

totipotent (any type, found in zygotes), pluripotent (any type but not whole organism, found in embryos), multipotent (most but not all types, found in adults)

what level of stem cells are found in plants

pluripotent

uses of stem cells in medicine

repair damaged tissues, treatment of neurological conditions like Alzheimer’s and Parkison’’s, research into developmental biology

how can stem cells be used in treatment of neurological conditions like Alzheimer’s and Parkison’’s

Stem cells can differentiate into various types of cells, including brain cells, potentially replacing damaged cells and improving cognitive function.

how can stem cells be used to repair damaged tissues

Stem cells can be guided into becoming specific cells that can be used in people to regenerate and repair tissues that have been damaged or affected by disease

how can stem cells be used to research into developmental biology

Before giving drugs in development to people, researchers can use some types of stem cells to test the drugs for safety and quality