CELL DIVISION, DIVERSITY, AND ORGANISATION

what is the cell cycle?

the highly ordered sequence of events that takes place in a cell, resulting in division of the nucleus and the formation of 2 genetically identical daughter cells

why do cells divide on a regular basis?

to bring about growth and asexual reproduction

describe the stages of the cell cycle

- period of non-cell division called interphase

- period of active cell division by mitosis

- division of cytoplasm following mitosis, resulting in 2 new genetically identical daughter cells called cytokinesis

during interphase, the cell is carrying out all its normal functions (e.g. respiration and photosynthesis) as well as....?

- increasing ATP production

- making new organelles and chemicals

- copying DNA

- checking DNA for mutations

cell cycle

look at diagram in notes

what happens during the M phase of the cell cycle?

metaphase checkpoint - mitosis and cytokinesis

What happens during the G1 phase of the cell cycle?

gap phase 1: cell grows and new organelles and proteins are made

what happens during the G1 checkpoint of the cell cycle?

checks that chemicals needed for replication are present and for any damage to DNA before entering S-phase

What happens during the S phase of interphase?

synthesis: DNA replication, ready to divide by mitosis

What happens during the G2 phase of the cell cycle?

gap phase 2: cell keeps growing and proteins needed for cell division are made

What happens during the G2 checkpoint of the cell cycle?

the cell checks whether all the DNA has been replicated correctly and without any damage. if it has, the cell can enter mitosis

what is the M checkpoint of the cell cycle?

spindle assembly checkpoint, check for alignment of chromosomes

What is apoptosis?

programmed cell death

when does apoptosis take place?

if any of the checks during the cell cycle fail

what are the main stages of mitosis?

1. prophase

2. metaphase

3. anaphase

4. telophase

what happens during prophase in mitosis?

- chromosomes condense (become shorter and fatter)

- centrioles move to the poles forming the spindle

- nuclear envelope/membrane breaks down

- nucleolus disappears

what happened during metaphase in mitosis?

- chromosomes (each with 2 chromatids) line up along the equator attached to spindle fibres by their centromeres

what happens during anaphase in mitosis?

- centromeres divide separating the sister chromatids

- spindle fibres contract, pulling chromatids to the poles (centromeres first)

what happens during telophase in mitosis?

- chromosomes uncoil

- nuclear envelope forms around each group of chromosomes

where does cell division occur in plants?

meristems (e.g. shoot tips and root tips)

do plants have centrioles?

no

what does cytokinesis in animal cells involve?

in animal cells, cytokinesis involves the plasma membrane "pinching in"

fill in the gaps.

In plant cells, a ____ ____ is laid down at the equator of where the spindle fibres were.

cell plate

what comes from the cell plate in plant cells?

new plasma membrane and cell wall

Fill in the gaps.

The 2 daughter cells produced in mitosis are both ----- ----- & will be able to carry out the ---- ------ as the original (parent) cell

The 2 daughter cells produced in mitosis are both genetically identical & will be able to carry out the same functions as the original (parent) cell

why do cells need to be able to divide?

- allow growth of tissues

- repair tissues

- to reproduce asexually (all offspring are genetically identical)

what is an advantage of asexual reproduction?

can happen quickly and many clones can be produced

what are examples of asexual reproduction in plants?

- strawberry plants & spider plants

- potatoes

fill in the gap.

For sexual reproduction, organisms need to make special sex cells called -----

For sexual reproduction, organisms need to make special sex cells called gametes

what are karyotypes?

Pictures that show the chromosomes that two people have

What is a zygote?

Fertilised egg

The chromosomes are all paired up, how many pairs do humans have?

23

which sex has xx chromosomes, and which has xy chromosomes

xx - female

xy - male

what is each chromosome pair called?

homologous pair

fill in the gaps.

Each chromosome pair is a similar ____ & ____, w/ a _______ in the same place.

Each chromosome pair is a similar size & shape, w/ a centromere in the same place.

where does one of each homologous pair come from?

one of each homologous pair comes from each parent

will each chromosome in a pair have the same genes present or different? And as a result will they be genetically identical or not?

each chromosome in a pair will have the same genes present, but will not be genetically identical

why are chromosomes in a pair not genetically identical, even though they have the same genes present?

they may contain different alleles (different forms of a gene) - a different base sequence = different sequence of amino acids

what is a haploid?

gametes with only 1 chromosome

what is a diploid?

2 gametes fuse to form a zygote

how many chromosomes do humans have and how many pairs?

46 chromosomes (23 pairs)

what does somatic cells mean?

body cells

how many copies of each chromosome do all somatic cells (except gametes) have and what are they called as a result?

all somatic cells (except gametes) have 2 copies of each chromosome & so are called diploid cells (2n)

how many copies of each chromosome do gametes have and what are they called as a result?

gametes only have 1 copy of each chromosome and are said to be haploid cells (n)

what are autosomes?

non-sex chromosomes

what is meiosis?

special type of cell division which produces gametes

fill in the gaps.

All gametes are _______ ______/different bc each cell contains only ___ copy of each chromosome which is a mixture from both parents.

All gametes are genetically unique / different bc each cell contains only 1 copy of each chromosome which is a mixture from both parents.

what happens during fertilisation?

- at fertilisation, the sperm cell nucleus (23) and the egg cell nucleus (23) join.

- the fertilised egg (zygote) now contains 46 chromosomes

- this maintains the correct chromosome number each generation (if the no. of chromosomes didn't halve, it would double each generation)

- refer to diagram in notes

During meiosis, genetic variation occurs as a result of...?

- crossing over of non-sister chromatids during prophase 1

- random arrangement & segregation (splitting) of bivalents (homologous pair of chromosomes) during metaphase 1

- random arrangement & segregation of sister chromatids during metaphase 2

- random mutation can occur, but this is NOT a valid explanation for why meiosis causes genetic variation

- the process of fertilisation also increases genetic variation bc it is a random process, whereby 2 genetically different sex cells fuse together

How many divisions of the cell does meiosis involve? What are they called

meiosis involves 2 divisions of the cell - meiosis 1 & meiosis 2

when the cell is not dividing during meiosis, what stage is it said to be in

interphase

what happens during interphase during meiosis?

The DNA content of the cell doubles and new cell organelles are formed

What happens during prophase 1 in meiosis?

- the chromosomes condense and are seen to have split into two chromatids

- the chromosomes shorten and thicken by coiling

- the paternal and maternal chromosomes come together in homologous pairs

- as the chromosomes pair up, they shorten and twist around each other, causing tension, and sections of chromatid may break off and exchange with corresponding sections of a different chromatid

- towards the end of the stage, the nucleolus disappears and the nuclear envelope breaks down

During prophase 1 in meiosis the paternal and maternal chromosomes come together in homologous pairs, what is this pairing called?

Synapsis

During prophase 1 in meiosis the paternal and maternal chromosomes come together in homologous pairs, what is each homologous pair called?

Bivalent

what does a bivalent consist of?

A bivalent consists of 4 strands; 2 chromosomes, each split into 2 chromatids

During prophase 1 in meiosis, chromosomes pair up, they shorten and twist around each other, causing tension, and sections of chromatid may break off and exchange with corresponding sections of a different chromatid. What are the points where this exchange of chromatid material occurs called? And what is this swapping of chromatid material called?

- the points by the exchange of chromatid material occurs are called chiasmata

- this swapping of chromatid material is called crossing over

What happens during metaphase 1 of meiosis

- at the start of this stage, the spindle will have formed

- the chromosomes assemble on the equator of the spindle

What happens during anaphase 1 of meiosis?

- the chromosomes in each bivalent separate and as a result each pole receives only one of each homologous pair of chromosomes

- the contraction of spindle fibres pulls the homologous chromosomes apart

- each pole receives a haploid number of chromosomes

What happens during telophase 1 of meiosis?

- the chromosomes reach the opposite poles of the spindle

- the nuclear envelope forms around each group of haploid chromosomes

- usually the chromosomes will remain condensed

- cytokinesis occurs to produce two haploid cells

What happens during prophase 2 of meiosis?

The new spindle fibres develop at right angles to the old spindle

What happens during metaphase 2 of meiosis?

- the separate chromosomes arrange themselves on the equator of the spindle

- each chromosome attaches to a spindle fibre by means of its centromere

What happens during anaphase 2 of meiosis?

- the centromeres divide

- the spindle fibres contract and pull the two chromatids to the poles, centromeres first

What happens during telophase 2 of meiosis?

- upon reaching the poles, the chromatids lengthen and become indistinct

- the spindle disappears and the nuclear envelope reforms

- cytokinesis takes place, resulting in four haploid cells, each with a different genetic make-up (genetically different to each other and parent cells)

what is division of labour?

each organelle in a cell has a different function to perform

why do cells become specialised?

to carry out a particular function

how do we go from cells --> organ system

- cells group together to form a tissue

- tissue can be grouped to form organs

- organs are grouped into organ systems

what are the 2 types of epithelial cells?

squamous epithelia and ciliated epithelia

What do epithelial cells cover?

The inner surfaces of organs

Why are some epithelial cells called simple?

Because the tissue is only one cell thick

What are epithelial cells held together by?

A basement membrane

What is a basement membrane made up of?

Collagen and glycoproteins

What is the thinner tissue of the body?

Epithelium

What is the surface of simple squamous epithelium cells like?

Smooth, flat and very thin

How do simple squamous epithelium cells fit together?

Like tiles

What do simple squamous epithelium cells provide?

Low friction surface

Simple School epithelium lines the inner surface of...?

- cheeks

- blood vessels

- atria

- ventricles

- walls of alveoli

Where is mucus produced?

Goblet cells

What does mucus do?

Mucus traps dirt and bacteria to prevent infection / damage to organs

What does cilia do?

Move mucus

What is the role of cilia in the bronchioles?

Moves mucus towards the throat so it can be swallowed

What is cartilage?

Connective tissue found in joints

What does cartilage do?

Shapes and supports ears, nose and windpipe

When is cartilage formed?

Cartilage is formed when cells called chondroblasts secrete an extracellular matrix (jelly-like substance containing protein fibres), which they become trapped inside

What is muscle tissue made up of?

Bundles of cells called muscle fibres

What are the three types of muscle and what do they do?

- skeletal > attaches to bone

- cardiac > heart wall (myogenic)

- smooth > blood vessels/airway/many organs

What are five examples of animal organs?

- Brain

- kidney

- biceps muscles

- heart

- liver

Name the 11 organ systems in the human body

- digestive system

- circulatory system

- respiratory system

- urinary system

- integumentary system

- musculoskeletal system

- immune system

- nervous system

- endocrine system

- reproductive system

- lymph system

What are the organs and tissues involved in the digestive system?

oesophagus; stomach, intestines & associated glands; liver & pancreas

What are examples of life processes carried out by the digestive system?

Nutrition to provide ATP & materials for growth & repair

What are the organ and tissues involved in the circulatory system?

Heart and blood vessels

What are examples of life processes carried out by the circulatory system?

Transport to and from cells

What are organs and tissues involved in the respiratory system?

Airways, lungs, diaphragm, and intercostal muscles

What are examples of life processes carried out by the respiratory system?

Breathing and gaseous exchange excretion

What are organs and tissues involved in the urinary system?

Kidneys, uterus and bladder

What are examples of life processes carried out by the urinary system?

Excretion and osmoregulation

What are organs and tissues involved in the integumentary system?

Skin, hair, nails

What are examples of life processes carried out by the integumentary system?

Waterproofing, protection, temperature regulation

What are organs and tissues involved in the musculoskeletal system?

Skeleton and skeletal muscles

What are examples of life processes carried out by the musculoskeletal system?

support, protection, and movement