Module 2, Chapter 6: Cell division, Cell diversity and Cellular Organisation

Cell Cycle
the process that all body cells in multicellular organisms use to grow and divide
Why are there 2 strands in a chromosome?
each chromosome has already made an identical copy of itself during interphase
two identical chromosomes that split and contain the same genetic material
How are the chromotids held together?
by the centromere
What does the cell cycle consist of?
- cell growth and DNA replication = INTERPHASE

- cell division = M phase

-----+ involving mitosis (nuclear division)

-----+ Involving cytokinesis (cytoplasmic division)
What is the M phase?
How is interphase divided?
- Gap Phase 1

- Synthesis

- Gap Phase 2
How is the Cell Cycle replicated?
by checkpoints
Where do the checkpoints occur?
occur at key points during the cycle to make sure it's okay from the process to continue
What does the G1 checkpoint do?
checks that chemicals needed for replication are present and for any damage to the DNA before entering S phase
What happens in the synthesis phase?
cell replicates its DNA ready to divide by mitosis
What happens in Gap Phase 1?
- cell grows

- new organelles and proteins are made
What happens in Gap Phase 2?
- cell keeps growing

- proteins needed for cell division are made
What does the G2 checkpoint do?
cell checks whether all the DNA has been replicated without any damage
What's the M phase?
mitosis and cytokinesis
4 Stages of Mitosis
Why is mitosis needed?
- needed for growth of multicellular organisms

- repair of damaged tissues
What happens in Interphase?
1. the cell carries out normal functions but also prepares to divide

2. the cell's DNA is unraveled and replicated to double its genetic content

3. he organelles are replicated, so it has spare ones

4. ATP content is increased (provides energy for cell division)
What happens in Prophase?
1. chromosomes condense, getting shorter and fetter

2. tiny bundles of protein (centrioles) start moving to opposite ends of the cell, forming a network of protein fibres across it called the spindle fibres

3. nuclear evolve breaks down and chromosomes lie free in the cytoplasm
What happens in metaphase?
1. the chromosomes (each with 2 chromatids) line up along the middle of the cell and become attached to the spindle by their centromere

2. at the metaphase checkpoint, the cell checks that all the chromosomes, are attached to the spindle before mitosis can continue
What happens in Anaphase?
1. the centromeres divide, separating each pair of sister chromatids

2. the spindles contract, pulling chromatids to opposite ends of the cell, centromere first
What happens in Telophase?
1. the chromatids reach the opposite poles on the spindle

2. they uncoil and become long and thin again

3. now called chromosomes again

4. a nuclear envelope forms around each group of chromosomes

5. 2 nuclei
What happens in Cytokinesis?
1. the cytoplasms divides

2. In animal cells, cleavage furrow forms to divide the cell membrane

3. 2 daughter cells that are identical to the original cell and to each other

4. Usually begins in anaphase and ends in telophase

5. seperate process to mitosis
What happens in Sexual Reproduction?
- in sexual reproduction, 2 gametes (egg and a sperm) join together to form a zygote

- zygote divides and develops into a new organism
a type of cell division that happens in reproductive organs to produce gametes
Cells that divide by Meiosis....
have the full number of chromosomes to start with, but the cells that are formed from meiosis have half the number
Haploid Cells
cells with half the normal number of chromosomes
Why are cells that are formed by meiosis all genetically different?
because each new cell ends up with a different combination of chromosomes
What divisions does Meiosis include?
Meiosis I and Meiosis II
What is Meiosis I?
the reduction division (halves the chromosome number)
How does Meiosis begin?
- with interphase

1. DNA unravels and replicated

2. produces double-armed chromosomes called sister chromatids
What happens in Prophase I
1. chromosomes condense, getting shorter and fatter

2. chromosomes arrange themselves in to homologous pairs and crossing over occurs

3. centrioles start moving to opposite ends of cell - forming spindle fibres

4. nuclear envelope breaks down
How many chromosomes do humans have?
46 (23 pairs)
Where do half of our chromosomes come from?
one chromosome in each pair came from the mother and one from the dad
Chromosomes that make up each pair.....
- same size

- same genes

- different alleles
Homologous Chromosomes
Chromosomes that have the same sequence of genes and the same structure
What happens in Metaphase I?
1. homologous pairs line up across centre of the cell

2. attach to the spindle fibres by their centromeres
What happens in Anaphase I?
1. the spindles contract, separating the homologous pairs

2. one chromosomes goes to each end of the cell
What happens in Telophase I?
a nuclear envelope forms around each group of chromosomes
What happens in Cytokinesis in Meiosis?
1. division of cytoplasm

2. 2 haploid daughter cells are produced
Prophase II
1. spindle begins to from

2. nuclear membrane breaks down
Metaphase II
chromosomes line up at equator
Anaphase II
1. chromatids are separated

2. each new daughter cell inherits one chromatid from each chromosome
Early Telophase in Meiosis
1. Nuclear Envelopes form

2. Cytoplasm divides

3. Cell membranes join up to from 4 genetically different haploid daughter cells are produced - these are gametes
Late Telophase in Meiosis
Chromosomes decondense and uncoil
How do Chromatids cross over in Prophase I?
1. chromatids twist around each other and bits of chromatids swap over

2. chromatids contain the same genes, but now have a different combination of alleles
Crossing Over of Chromatids
crossing over in meiosis I means that each of the four daughter cells formed from meiosis contains chromatids with different alleles
Independent Assortment of Chromosomes
1. each homologous pair of chromosomes in your cells is made up of one chromosome from your mother and father

2. when the pairs line up in metaphase I and are separated in anaphase I, it's completely random which chromosome from each pair ends up in which daughter cell

3. 4 daughter cells produced by meiosis have completely different combinations of those maternal and paternal chromosomes


5. his 'shuffling' of chromosomes leads to genetic variation in any potential offspring
Function of Neutrophil
- type of white blood cell

- defends body against disease
Neutrophil Adaptations
- flexible shape to engulf pathogens

- many lysosomes in their cytoplasms which contain digestive enzymes to break down the engulfed particles

- multi lobed nucleus to squeeze through small gaps to get to the site of infections
Function of Erythrocytes
- red blood cells

- carry oxygen in blood
Erythrocytes Adaptations
- biconcave disc shape increases surface area to volume ratio for gas exchange

- they have no nucleus, so there's more room for haemoglobin

- flexible to squeeze through narrow capillaries
Ciliated Epithelial Cell Function
- cells joined by interlinking cell membranes and a membrane at their base

- in airways

- move particles away
Adaptations of
Ciliated Epithelial Cells
- hair like structures on cilia that move in rhythmic manner = waft
Function of Squamous Epithelial Cells
- cells joined by interlinking cell membranes and a membrane at their base

- in lungs
Adaptation of Squamous Epithelial Cells
- very thin to allow efficient diffusion of gases
Function of Sperm
- male sex cells

- to get the male DNA to the female DNA
Adaptations of Sperm
- flagella to swim to egg

- lots of mitochondria to provide energy to swim

- acrosome contains digestive enzymes to enable sperm to penetrate the surface of the egg
Function of Palisade Cells
- present in the mesophyll

- do most of photosynthesis
Adaptations of Palisade Cells
- contain many chloroplasts to absorb a lot of sunlight

- thin walls, so CO2 can easily diffuse into cell

- rectangular box shaped to be closely packed to form continuous layer

- large vacuole to maintain turgor pressure

- chloroplasts can move within the cytoplasm in order to absorb more light
Root Hair Cells Function
- present at the surface of roots near the growing tips

- absorb water and minerals from the soil
Adaptation of Root Hair Cells
- root hairs that large surface area for absorption

- thin, permeable cell wall for entry of water and ions

- cytoplasm has extra mitochondria to provide the energy needed for active transport
How are Guard Cells found?
in pairs
What's the Stoma?
- gap between guard cells

- tiny pore in surface for gas exchange
Function of Guard Cells
in the light, guard cells take up water and become turgid
Adaptation of Guard Cell
- thin outer walls and thickened inner walls force them to bend outwards, opening the stomata

- cell wall is thicker on one side so cell does not change shape symmetrical as its volume changes
a group of cells (plus any extracellular material secreted by them) that specialised to work together to carry out a particular function
Where is the Squamous Epithelium Tissue Found
- alveoli

- lining of lungs
Adaptations of Squamous Epithelium Tissue
- thin due to flat cells that make it up

- one cell thick

- for rapid diffusion
Ciliated Epithelium Tissue
- a layer of cells covered in cilia

- found on surfaces where things need to be moved

- e.g. trachea, where cilia wafts mucus along
What is Muscle Tissue made up of?
made up of bundles of elongated cells called muscle fibres
What are Muscle Fibres
bundles of elongated cells
Function of Muscle Tissue
shorten in length (contract) in order to move bones, which in turn move the different parts of the body
Types of Muscle Tissue
- Smooth

- Cardiac

- Skeletal
Where are Smooth Muscle Tissue found?
lining the stomach wall
Where is Cardiac Muscle Tissue found?
What is Skeletal Muscle Tissue used for?
to move
What do Skeletal Muscle Tissues contain?
myofibrils, which contain contractile proteins
What is Cartilage Tissue?
type of connective tissue found in the joints
What does Cartilage Tissue contain?
fibres of the proteins: elastin and collagen
What does Cartilage Tissue support?
shapes and supports the cars, nose and windpipe
How is Cartilage Tissue formed>
when cells called chondroblasts secrete an extracellular matrix, which they become trapped inside
What is an Extracellular Matrix?
jelly like substance containing protein fibres
Adaptation of Cartilage Tissue?
firm and flexible
What are Xylem and Phloem Tissues?
vascular tissue
Function of Xylem Tissue
transports water and minerals up the plant
What is Xylem Tissue composed of?
vessel elements (elongated dead cells) and living parenchyma cells
How is xylem adapted?
cell walls are strengthened by lignin, which provide structural support
Function of Phloem Tissue
transports sugars around the plant
How is the Phloem Tissue arranged?
in tubess
What is Phloem Tissue made up of?
sieve cells, companion cells and ordinary plant cells
Sieve Plates
- phloem

- each sieve cell has end walls with holes in them, so can sap can move easily through them
a group of different tissues that work together to perform a particular function
Example of Organs
- lungs

- heart
What tissues do Lungs contain?
- squamous epithelial tissue (alveoli)

- ciliated epithelial tissue (bronchi)

- elastic connective tissue (blood vessels)

- vascular tissue (blood vessels)
What tissues do Leaves contain?
- contain palisade tissue (photosynthesis)

- epidermal tissue (prevent water loss)

- xylem and phloem tissues in veins
group of organs that work together to perform a life function
Organ System
Examples of System
- digestive

- cardiovascular

- gaseous exchange system
Reduction Division
meiosis I