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Unit 2: Biology

Topic 2: Cells

- Biology – The study of life.

What is Life? pp.411-414

- The properties of life:

1. Order

2. Reproduction

3. Growth and Development

4. Use Energy

5. Response to the environment

6. Homeostasis

7. Evolutionary adaptation

1. Order p. 549

Atoms

Molecules

Organelles

Cells

Tissues

Organs

Systems

Organisms

2. Reproduction- Organisms are able to make more organisms

like themselves.

- It is necessary to maintain population size.

- Basic reproduction is cell division that occurs

at the cellular level.

- Reproduction is achieved in different ways:

1. Sexual reproduction- A type of reproduction

in which two parents produce offspring that have

unique combinations of genes.

2. Reproduction 2. Reproduction

2. Asexual reproduction – A type of

reproduction involving only one parent that

produced genetically identical offspring.

E.g. budding.

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- Growth - The increase in the size or number of

cells.

- Development - The pattern of growth. I.e.

changes in the shape.

- Both are determined by DNA.

3. Growth and Development

5. Response to the Environment- Each organism interacts continuously with

its surroundings.

4. Energy Utilization (Metabolism)

- Metabolism- The total of all reactions in a cell.- Chemical reactions are controlled by DNA.

6. Homeostasis- Homeostasis – Maintaining a stable internal

environment.

- I.e. keeping everything inside an organism the

same.

- E.g. If it is too hot, we sweat. The water

evaporates and we feel cooler. If it is too cold

we shiver. The movement of muscles

generates heat.

7. Evolutionary Adaptation-Evolution – Populations change over time.

-One way change can happen is natural

selection.- Natural selection – A Process for deleting

unsuitable characteristics. It produces well

suited or adapted individuals .

- Macromolecules – Large molecules.

- The main macromolecules for life are:

1. Carbohydrates

2. Lipids

3. Proteins

4. Nucleic acids

Chemical Components of Cells

pp. 412 - 414 – Carbohydrates contain lots of carbon and

hydrogen.

- A very important subcategory are sugars.

- Some sugars are small and important to

provide energy.

- E.g. glucose

1.Carbohydrates

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- Some sugars are very large and are used as

storage material (starch, glycogen), others are

building materials (cellulose, chitin).

1.Carbohydrates- All are hydrophobic.

- There are three types:

A) Fats - Large molecules made of glycerol

and fatty acids. Their main function is to store

energy.

- 1g of fat stores more than twice as much

energy as 1g of carbohydrate.

- If the molecule is solid at room temperature

it is usually saturated and called a fat.

- If the molecule is liquid at room temperature it is unsaturated and called an oil.

2. Lipids

B) Phospholipids – These are important parts

of cell membranes. They form a double layer

(lipid bilayer) that block many things from

passing through.

They have a polar “head” and two non-polar

“tails.”

2. Lipids

C) Steroids – These form the basis of some

hormones and cholesterol.

- Cholesterol is an important part of animal

cell membranes which helps it stay fluid

(moveable) in warm and cold temperatures.

2. Lipids

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-Very important macromolecules.

-Proteins make up 50% of the dry weight of

most cells.

-Proteins are polymers made up of amino

acids.

-The number and type of amino acids determine

the 3D shape of the protein and it is this shape

that determines its function.

-Protein functions include support, transport,

movement, defense, and enzymes.

- Enzymes – Proteins that speed up chemical

reactions without reacting themselves.

3. Proteins

-They are made up of smaller parts called

nucleotides.

-These molecules enable living organisms to

reproduce their complex components from one

generation to the next.

-E.g. DNA, Ribonucleic acid (RNA).

4. Nucleic Acids Types of Cells pp.420-422

- There are two types of cells

1. Prokaryote - No nucleus nor organelles. E.g. Bacteria.

- They are small and single celled.

2. Eukaryote – True nucleus containing genetic material. Organelles are present. E.g. Animal cells, plant cells, fungi cells.

- They are larger and more complex than prokaryotic cells. They can be found in some single celled organisms or in multicellular organisms.

Prokaryotic cell Eukaryotic cell – Animal

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Eukaryotic cell – Plant

-Organelle – Small bodies inside of cells

with specialized functions. They are

surrounded by membranes and found only

in Eukaryotic cells.

-E.g. Mitochondria.

-Organelles are found inside the cell

membrane, in the cytoplasm (gel-like fluid

that makes up most of the cell’s volume).

Types of Cells

- Examples of organelles:

1. Nucleus – Contains DNA.

2. Endoplasmic Reticulum (ER) – Two types:

Smooth ER – Makes lipids and

membranes.

Rough ER – Make proteins.

3. Golgi apparatus – Receives products from

the ER then sorts, stores and ships them off.

Types of Cells4. Lysosome – Breaks down organic material.

5. Mitochondria – Produces energy for the cell to

use.

6. Chloroplast – In plant cells, they make sugar

using light energy.

Other non-organelle structure include:

1. Ribosomes – Make proteins.

2. Cytoskeleton – Cell skeleton. Helps the

cell keep its shape.

Types of Cells

Fig. 15.11

The Cell Membrane pp.421-426

• Cells need to move nutrients in and

wastes out.

• How the movement is done depends on

the properties of the particle and always

involves the cell (plasma) membrane.

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Cell Membrane

• Cell Membrane – Surrounds the cell and controls what materials enter or leave the cell.

• It is made of a phospholipid bilayer, proteins, carbohydrates, and cholesterol.

• The structure of the cell membrane only allows small or non-polar (not charged) molecules to pass freely through.

• E.g. O2, H2O and fats can pass through.

The Plasma (cell) membrane

Cell Transport pp.421-426• There are a variety of ways cells can move

things across their plasma membrane.• 1. Diffusion – Small, or non-polar molecules

can freely pass through the plasma membrane without using energy.

• These molecules will pass over the membrane until there are equal concentrations on both sides.

2. Osmosis - The flow of solvent (usually

water) through a semipermeable membrane.

- Osmosis is essentially the diffusion of water

from an area of high concentration (lots of

water), to an area of low concentration (little

water).

Cell Transport

Cell Transport

• 3. Facilitated Diffusion – Some molecules can not pass through the phospholipid bilayer.

• Sometime cells have special protein channels (doors) that will let these molecules pass through.

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Cell Transport• 4. Active transport – When a cell uses energy

to move materials across it’s membrane againsta concentration gradient (i.e. up hill).

• Sometimes a cell wants to get rid of a lot of a chemical (e.g. waste) or wants to store a lot (e.g. sugar).

• If the cell just opened a protein channel, the chemical would move until it is equal on both sides.

• To have more on either side, cells use special protein channels that actively “grab” a specific chemical and “pump” it into or out of the cell.

• This process requires energy.

Cell Transport• 5. Endocytosis & Exocytosis – Movement

of large particles across the cell membrane.• Protein channels can only move molecules

through the cell membrane.• White blood cells eat bacteria and cells in the

digestive system release large enzymes.• Both cases require movement of large

particles.

• Endocytosis – Movement of large particles into a cell.

• Exocytosis – Movement of large particles out of a cell.

Microscopes pp.417-418

- The development of the microscope was the

key to understanding that all living things are

made of cells.

- Early microscopes were basically magnifying

glasses.

- Today we have several much more powerful

types of microscopes:

- 1. Compound Light Microscope – Can

magnify up to about 1000x.

- These microscopes pass light through thin

slices of specimens.

Microscopes

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Microscopes

- 2. Stereomicroscope (Dissecting

microscope) – Can magnify up to about

100x.

- These also use light to see 3D images of

larger objects.

Microscopes pp.325-327

- 3. Transmission Electron Microscope

(TEM)– Can magnify up to about 50000x.

- These microscopes pass electrons through

very thin slices of specimens.

- These microscopes can be used to see

organelles.

Microscopes pp.325-327

- 4. Scanning Electron Microscope (SEM) –

Can magnify up to about 5000x.

- These also use electrons to see 3D images or

the outside of small objects.

Cell Communication pp. 426-427

- Cells sometimes need to communicate with

other cells.

- There are several ways this can be done:

- 1. Gap junctions – Allow messages travel

from one cell to an adjacent cell. Gap

junctions allow muscles to contract

simultaneously.

Cell Communication

- 2. Hormones – Messenger molecules that

can be sent around the organism.

- These only affect “target” organs or cells that

have specific receptors for that hormone.

- Hormones are especially effective when a

long lasting change is required.

E.g. testosterone, estrogen.

Cell Communication

- 3. Nerve Impulses – Electrical signals found

only in animals.

- These are used to send signals quickly and

for only a short time.

- E.g. a reflex.

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How Cells Reproduce pp. 427-430

- Cells do not live forever. Cells in the human

body may live a few months or last years.

- To replace these dying cells, grow, make

repairs, and reproduce, organisms need to

produce new cells.

- Most cells reproduce asexually using mitosis.

How Cells Reproduce- The life of a cell can be divided into two

categories:

1. Time spent reproducing (mitosis or meiosis)

2. Time spent not reproducing (interphase)

- Interphase can be subdivided further:

1. G1 Phase – Gap 1. Growth and metabolic activity occur.

2. S Phase – Synthesis phase. DNA is copied in preparation for cell division.

3. G2 Phase – Gap 2. Time between DNA being copied and actual cell division.

Fig. 15.26How Cells Reproduce

- Mitosis makes exact copies of eukaryotic cells and occurs in 4 stages:

1. Prophase – Long sections of DNA called chromosomes wind around proteins called histones to form thick X shaped structures. The nucleus dissolves.

2. Metaphase – The chromosomes line up along the equator of the cell.

3. Anaphase – The legs of each X shaped chromosome separate. They move to opposite ends of the cell.

4. Telophase – New nuclei begin to form.

How Cells Reproduce

- Cytokinesis – The cytoplasm of the

“mother” cell separates creating two new

“daughter” cells.

- Separate from mitosis and happens after.

Fig. 15.27