UNIT 4: CELLS

INDEX1. Levels of Organisation2. Cell theory3. The basic Unit of Life4. Types of Cells5. Eukaryotic Cells6. Cell Division

Atom

Molecule

Macromolecule

Cell

Organisms of the samespecies

Many populations together

All the living things on Earth

H2O

H, O

C6H12O6

animal cell

lungs

horse

herd of horses

praire

1. Levels of Organisation

2. Cell Theory (1838, Schleiden and

Schwann)

A cell is the smallest and simplest living thing.All cells come from other preexisting cellsThe cell is the basic structural and functional unit of life

All living things are made up of cells

Each of the cells that make up an organismcan function independently although they worktogether in a coordinated way

They can perform the three vital functions

3. The Basic Unit of Life

Main Parts in Every Cell

Membrane

It separates the cellfrom the environment

It controls substanceswhich enter and pass

out of the cell

CytoplasmSemi-liquid interior

which containsbiological molecules

Genetic material. DNA

It controls cellularactivity and gives the

cell its specificcharacteristics

Nutrition

The cell takes molecules from the environment and transforms

them into energy or new structures, by means of the metabolism.

Waste products are expelled.

Metabolism = chemical reactions which take place inside cells

Interaction

Cells:

• Detect environmental changes

• Respond to these changes

Phagocytosis

Reproduction

Formation of new cells. Daughter cells are alwaysidentical to their parent cell.

Activities 3, 7, 12, 13 page 69

4. Types of cell

Size

Bacteria (prokaryotic)

less than 3µm

Eukaryotic 5 µm - 20 µm

Complexity

Prokaryotic

DNA floating in the cytoplasm

No cellularorganelles with

membranes

Eukaryotic

DNA inside thenucleus

Cellularorganelles

Shape

bacteria

5. Eukaryotic cellsORGANELLE FUNCTION DRAWING

Endoplasmicreticulum

It makes and transportslipids and proteins

Golgiapparatus

It takes substancesfrom the endoplasmicreticulum and packs them into vesicles

ORGANELLE FUNCTION DRAWING

Lysosomes Digestion

Vacuoles Storesubstances

Ribosomes Synthesis of proteins

ORGANELLE FUNCTION DRAWING

Centrosome Productionof microtubules

Centrioles(animal cell)

They are involved in reproductionand cellmovement

Mitochondria Cellularrespiration(obtainenergy)

ribosomes

ORGANELLE FUNCTION DRAWING

Chloroplast(plant cell)

Photosynthesis(obtainglucose)

Nucleus It contains thegeneticmaterial (DNA), calledchromatin

Nucleoolus Synthesis of ribosomes

(with chlorophyll)

(double membrane)

ORGANELLE FUNCTION DRAWING

Cilia and flagela

Movement. They are controlled bythe centrioles

Cytoskeleton Protein fibres(tubules, microtubules…) whick keepand give shapeto the cell

PLANT CELL ANIMAL CELL

Cell wallChloroplastNO centriolesA big vacuole

NO cell wallNO chloroplastCentriolesSmall vacuoles

Activities 20, 21, 24 page 75

6. Cell Division (eukaryotic cells)

GOAL: to produce new cells in order to:

Grow and achieve embrionic development

Repair body’s tissues

The parent cell needs to have TWO COPIES of its

genetic material

original DNA

identical copied DNA

Daughter cells are IDENTICAL

Cytokinesis is the division of the cytoplasm

Mitosis is the division of the nucleus in four stages:

Prophase Metaphase Anaphase Telophase

Interphase is the preparation for the cellular division:

(it obtains nutrients, grows, copies the DNA and the centrosomes…)

Structure of a chromosome

A. Prophase

The chromosomes appear (chromatin condenses)The nucleolus disappearsThe mitotic spindle appears (made up of protein fibers)The nuclear membrane disappears

B. Metaphase

The chromosomes connect to the mitotic spindle withtheir centromeres and line up along the middle of the cell.

Mitotic spindle

e

C. Anaphase

The spindle fibres contract and pullthe chromatids to the opposite polesof the cell. Chromosomes’ centromeres breakand sister chromatids separate.

D. Telophase

Chromatids arrive to the poles of the cell.The mitotic spindle disappears.A nuclear membrane surrounds each group of chromosomes.The chromatids become chromatin.The nucleolus reappears.

E. Cytokinesis (division of the cytoplasm)

ANIMAL CELLS cytoplasm streches

PLANT CELLS a wall called cell plate foms

2 daughter cells

GOAL: To produce gametes, which are haploid cells (they just have the half of the chromosomes)

n = haploid Reproductive cells

2n = diploid Somatic cells

Gametes: ovum and spermatozoon

The rest of the cells of the body

The gametes (ovum and spermatozoon) have only one of the homologous chromosomes.They are haploids (n)

The cells with pairs of homologous chromosomes are diploid (2n)

n

n

+ 2n

zigote

Each chromosome belonging to each of the pair of homologous chromosomeshas been supplied by one of theparentals.

Every cell of the new living being are diploid

+

Zigote (2n)

Spermatozoon (n)

Ovum (n)

In this example:

2n=6

n=3

In human beings

2n=46

n=23

Mitosis, mitosis….

Embryo (2n)

Adult (2n)Meiosis!

Double information for everycharacter.

Chromosomes are in pairs. They are called homologous chromosomes

Blue eyes Brown eyes

A GroupB Group

or

The result of the meiosis is a huge genetic biodiversity, this is, all thegametes are different among them, because many combinations are possible:

Blue eyes

Blue eyes

B Group

B Group

Brown eyes

Brown eyes

A Group

A Group

Meiosis is the process of cell division when a diploid cell (2n) divides into 4 daughter haploid cells (n)

Testicles and ovaries are somatic cells diploid (2n)

How can they produce reproductive cells, which are haploid (n)???

46 in human beings / 6 in our example

23 in human beings / 3 in our example

• 1st division chromosomes are separated2 cells n

• 2nd division chromatides are separated4 cells n

Meiosis includes two consecutive

cell divisions:

1st Division: Reduction division We obtain cells with half the numberof chromosomes

A. Prophase I

Chromosomes appear in pairs (homologous chromosomes)

A A 0 0 A A0 0

Crossing over

Homologous chromosomes exchange genetic material by crossing over:

B. Metaphase I

Pairs of homologous chromosomes become attached to the spindle fibres.

C. Anaphase I

Complete chromosomes are pulled to each spindle pole the number ofchromosomes in every cell has been reduced to the half.

C. Telophase I

As a result two daughter haploid cells appear. Nuclear envelopes appearand the chromosomes transform into chromatin.

A short interphase takes place and the second division starts:

2nd Division: Normal mitosis Chromatids are separated. At the end, cytoplasm divides, too.

http://www.dailymotion.com/video/xkf13m_meiosis-interphase_tech

Result: 4 different haploid (n) cells (reproductive cells/gametes)

1st division

2nd division

Page 78 activity 26

Page 80 activity 27

Page 82 activity 3, 6, 7, 8, 9

Development of Basic Competences page 83 (both)

Glossary:

• Haploid

• Diploid

• Somatic cell

• Chromatid

• Homologous chromosomes

• Synthesise