Chapter 2

cells

the smallest structure that can perform life’s functions.

Cell theory

all organisms are made of cells, which are the basic unit of life and arise from preexisting cells

Cell membrane (2)

separates cell contents such as organelles from the environment outside of the cell and from neighbouring cells

selectively permeable - only certain substances can pass through

Cytoplasm (3)

Jelly-like or watery material inside cell

fills all the space between the nucleus and the cell membrane

organelles are suspended within

cytosol (5)

liquid part of cytoplasm

most metabolic reactions occur here

controls osmotic pressure of cell

controls flow of chemicals in/out of cell

Organelles (3)

structures within cell that are specialised for particular functions. many are formed by cells internal membranes

Nucleus (7)

• sturcture

• function

STRUCTURE:

• largest organelle in the cell

• ovoid or spherical

• separated from cytoplasm by its own double membrane (nuclear membrane)

• DNA and nucleolus are suspended in jelly like substance called nucleoplasm

• contains nuclear pores: gaps in membrane that allow large molecules (e.g messenger RNA) to enter/exit the nucleus

• DNA and nucleolus are suspended in jelly like substance called nucleoplasm

FUNCTION

• includes DNA/genetic material, determines type of protein made, so controls structure and function of cell.

• nucleolus produce and assembles the cell's ribosomes

Ribosomes (3)

small and spherical organelles

where amino acids are joined together to make proteins

free in cytoplasm OR attached to ER

Endoplasmic reticulum (5)

parallel membranes that extend from cell membrane to nuclear membrane

provide surface for chemical reactions such as protein synthesis

channels store + transport molecules

rough endoplasmic reticulum: ribosomes attached to outside of some membranes

smooth endoplasmic reticulum: no ribosomes attached to the outside

Golgi Body (5)

flattened membranes stacked upon one another

found near nucleus

proteins produced at ribosomes pass through ER channels to Golgi Body to be modified and packed for secretion

small sacs of liquid containing proteins (vesicles) are formed at edges of Golgi Body membrane

Lysosomes (5)

small spheres formed at golgi body

contain digestive enzymes that can break down large molecules

lysosomes join with vesicles within cytoplasm and digest materials within

digest worn out organelles in a similar way

Mitochondria

spherical and sausage shaped structures spread throughout cytoplasm

glucose plus oxygen forms carbon dioxide plus water + chemical energy is the cellular respiration reaction, which occurs in mitochondria'

double membrane: outer membrane is smooth and surrounds mitochondrion, inner membrane folds to increase surface area for cellular respiration to occur

Cilia and flagella (3)

fine projections which can move the cell or move substances over the surface of the cell

cilia: short and numerous, resembling tiny hairs. found in lining of small intestine and oesophagus

flagella: longer, only one or two, found on sperm cells

Cytoskeleton (4)

structure that consists of microtubules and microfilaments to give the cell its shape

microtubules: hollow rods that keep organelles in place or move them around the cell

microfilaments: move materials around the cytoplasm and move the whole cell

centrioles are pairs of cylindrical structures involved in reproduction of the cell

Inclusions

chemical substances that are not part of cell structure but found in cytoplasm

e.g haemoglobin, melanin

Extracellular fluid (3)

fluids that surround a cell

separated from intracellular fluid by the cell membrane

allows for continual exchange of materials into and out of cells

Homeostasis

The maintenance of a

relatively constant internal environment

despite fluctuations in the external

environment

All cells need a supply of (6)

Oxygen for cellular respiration

Glucose for cellular respiration

lipids

vitamins and minerals

carbohydrates

proteins

All cells need removal of

Carbon dioxide

Water

Other waste products

useful substances which must exist the cell, such as hormones and enzymes

Function of Cell membrane

Physical barrier between extra/intracellular fluid because both are composed of different concentration of substances

Regulation of movement of materials both into and out of the cell (e.g entry of ions and nutrients, removal of wastes, release of secretions)

CM is first part of cell to be affected by changes in EX fluid (e.g hormones)

Support, as the internal part of CM is attached to microfilaments of cytoskeleton. membranes also attached to membranes of adjacent cells, supporting the tissue the cell are a part of

The model used to describe the cell membrane

Fluid Mosaic Model

FLUID: molecules are constantly changing position

MOSAIC: made up of many different kinds of molecules present

Structure of Cell Membrane

Phospholipid molecules (main structure): arranged in two layers known as bilayer

each molecule has a head that is hydrophilic, tail is hydrophobic,

heads on outside, tails on inside,

drift from place to place with heads and tails moving, keeping membrane fluid

What is embedded in the membrane and why

Cholesterol molecules that are wedged between phospholipids

• to make membrane less permeable to small water-soluble molecules that would otherwise freely cross

some protein molecules pass through membrane, while others just bound to surface

Membrane proteins

Receptor proteins: Respond to changes in extracellular fluid

Channel proteins: water soluble substances are free to pass through

Carrier proteins: Bind to particular molecules allowing them passage through membrane

Cell identity markers: Allow cells to recognise cells of the same tissue and foreign invaders

What are cell membranes described as? What does this mean? (2)

differentially permeable, semipermeable or selectively permeable.

allow certain ions and molecules to pass through, but restrict movement of others

how do materials pass through the cell membrane?

Active processes and Passive processes

Active processes

require the use of energy in the form of ATP

Passive processes

do not require energy

Simple diffusion

A passive process by which substances move from areas of high concentration to low concentration (move WITH the concentration gradient) without the use of membrane proteins

Concentration gradient

Difference in concentration that brings about diffusion

Steeper gradient - faster diffusion

What is simple diffusion more correctly known as?

Net diffusion, s some molecules may move against the concentration gradient. Once concentrations are the same, the same number of particles will be moving in each direction

What can easily enter cells via diffusion? Why?

Alcohol, steroids, fat soluble substances because they can diffuse through the lipid portions

Oxygen and Carbon Dioxide can enter too by diffusing through phospholipid bilayer

Why does Oxygen and Carbon Dioxide diffuse?

Oxygen is used up in cell for cellular respiration. There’s a lower concentration of oxygen in the cell than outside, therefore oxygen diffuses into the cell

Carbon Dioxide is produced from cellular respiration, so there is a high concentration of carbon dioxide outside than inside, therefore carbon dioxide diffuses out of the cell

What is Osmosis?

The diffusion of water molecules through a differentially-permeable membrane from an area of high water concentration to an area of low concentration

Example of Osmosis

Water will move from an area where solute is low to an area where solute is high to reach an equilibrium, meaning equal water to solute ratio

when water moves out of an area with low concentration of solute, it’s concentration of solute will increase because there is less water

What molecules can’t cross the bilayer? Why are water molecules able to?

Polar molecules (molecules that have a charge difference) such as glucose and sodium ions are unable to cross bilayer due to being repelled by non-polar tails

Water molecules are small enough to fit in between lipid tails

Types of solutions and how cells react to them

Hypertonic: Solution outside of cell has higher solute concentration that inside cell. water diffuses out, cell shrinks

Hypotonic: Solution outside of cell has lower solute concentration than inside cell. Water diffuses in, cell swells

Isotonic: Solution outside the cell has equal solute concentration as inside the cell. Cell stays the same, no net movement of water

Osmotic pressure

The pressure caused due to differences in concentration on either side of the membrane

high concentration of solute = higher pressure

Facilitated transport

Proteins in the cell

membrane allow molecules to be transported

across the membrane

What are the proteins that are used in Facilitated Diffusion?

Channel proteins that form protein channels

Carrier proteins that allow carrier mediated transport

What are Channel proteins? what do Protein Channels do? (4)

A pathway through a protein channel that allows the passage of substances through the membrane

Allow water-soluble particles to pass through

provide pathways for hydrophillic particles to pass through without getting repelled by hydrophobic tails

small in diameter, water ions can easily get through

Carrier mediated transport, and how it works

Transport of

ions or molecules across a cell membrane by

special carrier proteins

Open on one side of the membrane at a time.

Specific substance binds to binding site. Protein undergoes a conformational change and changes shape and opens the other side. Substance is then released on to the opposite side where it entered from.

Important characteristics of Carrier Proteins

Specific: Will only bind to particular molecules

Saturation: Once all available carriers are occupied, any increase in concentration of molecules to be transported cannot increase rate of movement

Regulation: Activity is regulated by substances such as hormones, which coordinate the activities

Two types of carrier mediated transport

Facillitated Diffusion

Active Transport

Carrier mediated facilitated diffusion

Transported through protein along concentration gradient, passive

Molecule attaches to binding site of protein. Protein changes shape and molecule is released

Active transport

Energy in the form of ATP

Against concentration gradient

Similar to facilitated diffusion, but doesn’t depend on concentration gradient

Cell can take in or pass out substances regardless of concentration

Vesicular transport

The transport of

materials into or out of a cell in membrane-bound

sacs called vesicles also called bulk transport

Active process, energy is needed from cell to form vesicles

Endocytosis

The process by which a cell

takes in materials by enfolding and enclosing

them; includes phagocytosis and pinocytosis

cell membrane folds around droplet of L/S particle until fully enclosed. Vesicle is formed, pinches off and suspended in cytoplasm

Exocytosis

The process whereby the

contents of the vesicles of cells are pushed

out through the cell membrane

Vesicle formed inside cell migrates to the membrane and fuses with it. Contents are then pushed into extracellular fluid

Phagocytosis

The process by which a cell

surrounds, and takes in, solid particles

Pinocytosis

The process by which cells

enfold, and take in, drops of liquid

What substances are transported in simple diffusion?

Water, Oxygen, CO2, fatty acids, steroids, ions such as sodium, lipids, soluble drugs

What substances are transported in Osmosis?

Water

What substances are transported in Facilitated diffusion?

Glucose, Amino acids

What substances are transported in Active Transport

Certain Ions, glucose, amino acids

What substances are transported in Endocytosis

Cholesterol, iron ions, microorganisms and cell debris or microorganisms by specialised cells

What substances are transported in Exocytosis

Secretions such as mucus and digestive juices

Movement within the cell is done through

Diffusion and structures

Diffusion

As diffusion spreads out particles, other molecules of a substance are used up in one part of the cell and other molecules will spread to take their place

e.g oxygen used in mitochondria for cellular respiration, lower concentration of oxygen in cell, oxygen will diffuse into area of lower concentration

Structure

e.g ER transports protein that it makes to Golgi Body for secretion.

Microtubules maintain shape and hold organelles but also guide organelles or molecules to places. Not permanent structures, break down and rebuild as needed

Surface area to volume ratio and their effects on cells (3)

Small cells have larger SA:V ratio than large cells

large cell would not be able to support itself because it would not have enough surface area to absorb nutrients/remove wastes produced for its large volume

as cell grows, ability to exchange enough materials to support it’s volume will diminish, because volume increases at a greater rate than surface area

Four structural levels of an organism

1) Cells

2) Tissue

3) Organs

4) System

Cells

lowest level

specialised to carry out functions (e.g muscle cells shorten, red cells transport oxygen)

Tissues

A group of cells that are similar in

structure and function

Organs

Structures made up of different types of tissue working together

2 or more tissues

stomach has epithelial tissue on inside and muscle tissue on walls

System

Group of organs that work together for a common purpose

e.g respiratory system supplies oxygen and removes CO2 from blood

all systems integrated into organism

Types of tissue

Epithelial tissue

connective tissue

muscular tissue

nervous tissue

Epithelial tissue

• what is it

• where is it found

• structure

Covering or lining tissue

FOUND IN:

Outer layer of skin

covering of heart, kidney lungs and intestines.

Inner lining of hollow organs such as stomach

STRUCTURE:

closely joined together

vary from thin and flat, to column or cube shaped

smooth surface

Connective tissue

Provide support, holds all body parts together

FOUND IN:

bone

cartilage

tendons

ligaments

adipose

blood

STRUCTURE:

not close together, separated by non-cellular material called matrix (blood’s matrix is the liquid the cells are suspended in)

Muscular tissue + types of muscular tissue

Made up of muscle fibres that are long and thin and can shorten in length to become shorter

skeletal muscle tissue, smooth muscle tissue, cardiac muscle tissue

Skeletal muscle tissue (4)

muscles attached to bones

voluntary muscle

striations, stripe-like

Smooth muscle

non-striated

walls of stomach, blood vessels, uterus, iris of eye

involutary

Cardiac muscle

makes up most of the heart

contractions = pumps

involuntary

Nervous tissue

made up of neurons

long projections from body of cell

stimulation = messages carried along projections from one part of the body to another

found in brain, spinal cord and nerves

Body systems

digestive

respiratory

circulatory

excretory

nervous

endocrine

skeletal

muscular

immune

reproductive

Digestive

ingestion, breakdown and absorption of food

Respiratory

Intake oxygen, remove CO2

Circulatory

transport nutrients, oxygen and wastes to/from cells

Excretory

removal of wastes

Nervous

Detection of environment changes, coordination

Endocrine

regulation and coordination of body activities

Skeletal

support and protect body parts

muscular

movement and support

Immune

protection against infection by micro-organisms

Reproductive

Production of new individuals

Secondary functions example

bones store minerals and produce blood cells AND provide support and protection

The organisms

all systems are interconnected

heart needs oxygen from respiratory system. brain needs nutrients absorbed by digestive system and transported by circulatory