Biology Notes - Chapter 3

SECTION 1

Living things come in all sizes.

o For example the blue whale and a tadpole. They do have cell size in common.

So, if the cells are the same size then why is there such a big difference in the

size of the tadpole and blue whale? The number of cells is what is different.

The blue whale has more

o Almost all cells are too small to see without the aid of the microscope

regardless of the size of the organism.

One of the first concepts to be developed in biology was the Cell Theory.

Cell Theory states the following

1. All organisms are made of cells

2. All existing cells are produced by other living cells.

3. The cell is the basic unit of live.

Contributors to the Cell Theory

o Robert Hooke was the first to identify cells and named them.

o Anton van Leeuwenhoek made lenses for the microscope and was able to

better view cells.

o Matthias Schleiden was the first to say plants are made from cells.

o Theodor Schwann concluded that all living things are made up of cells.

o Rudolf Virchow proposed that all cells come from other cells.

Cells can be separated into two categories based on their internal structures.

1. Prokaryotic Cells – do not have a nucleus or other membrane bound

organelles. The cell’s DNA is suspended in the cytoplasm. All prokaryotes are

microscopic single celled organisms.

2. Eukaryotic Cells – have a nucleus and other membrane bound organelles.

The nucleus encloses the genetic information or DNA. Eukaryotes may be

multicellular or single celled organisms.

SECTION 2

Eukaryotic cells have highly organized structures, including membrane-bound

organelles. Plant and animal cells share many of the same types of organelles, but

both also have organelles that are unique to their needs.

Cytoskeleton – a network of small proteins, long threads or fibers that

crisscross the entire cell and are constantly changing to meet the needs of

the cell.

o Types of fibers that make up the cytoskeleton are

Microtubules which are long hollow tubes that give the cell its

shape and act as tracks for movement of organelles. Maintains

cell shape.

Intermediate filaments which give the cytoskeleton strength

Microfilaments are the smallest and enable the cells to move and

divide. Gives the cell a sturdy, flexible framework.

Cytoplasm – jellylike substance that contains dissolved molecular building

blocks.

Cytosol – fluid portion of the cell and is mostly water. The water is used as a

solvent for the chemical reactions that are taking place in the cytoplasm.

Nucleus – the storehouse for most of the genetic information, or DNA, in

your cells. It is also known as the control center of the cell. This the largest

and most visible organelle.

Nuclear envelope – double membrane surrounding the nucleus.

Nucleolus – a dense region of the nucleus where tiny organelles essential for

making proteins, or ribosomes, are assembled.

Endoplasmic reticulum – an interconnected network of thin folded

membrane and is a large part of the cytoplasm. Involved in protein synthesis.

o Rough endoplasmic reticulum – ER studded or covered with ribosomes

o Smooth endoplasmic reticulum – ER that does not contain ribosomes. It

makes lipids and performs specialized functions for the cell.

Ribosomes – small round structures. Can be on the surface of ER or floating

freely in the cytoplasm.

Golgi apparatus – closely layered stacks of membrane enclosed spaces that

process, sort and deliver proteins. May also be called the Golgi complex.

Involved in protein packaging and delivery.

Vesicles – small membrane bound sacs that divide some materials from the

rest of the cytoplasm and transport these materials from place to place

within the cell. Short lived and formed and recycled as needed.

Mitochondria – bean shaped and have two membranes and involved in

energy production for the cell. They have their own ribosomes and DNA

which suggests that they were once free living.

Vacuole – fluid filled sac used for the storage of materials needed by a cell.

Most animal cells contain many vacuoles where plant cells contain a central

vacuole which takes to most of the space in the cell. In a plant it’s filled with

a watery substance that helps give the plant strength and support the entire

plant.

Lysosomes – membrane bound organelles that contain enzymes. They break

down damaged or worn out cell parts. Animal cells have numerous ones.

Centrioles – cylinder shaped organelles made of short microtubules arranged

in a circle. Form cilia and flagella.

Cell walls – rigid layer that gives protection, support, and shape to a cell. Only

found in plant cells.

Chloroplasts – organelles that carry out photosynthesis, making energy from

the sun and found in plant cells.

Cell membrane – also known as a plasma membrane that is flexible and

separates the inside of the cell from the outside of a cell. It protects the

internal structures and regulates movement of materials into and out of the

cell.

Chloroplast vs Mitochondria

Similarities

convert energy

have its own DNA

enclosed by two membranes

oxygen (O2) and carbon dioxide (CO2) are involved in its processes

have fluids inside of it

Differences

Chloroplast

plural: chloroplasts

usually found in plants and unicellular organisms

converts solar/light energy into chemical energy (sugar)

process is photosynthesis: composed of Light Reactions and Calvin Benson Cycle

has three compartments(parts): thylakoids (traps sunlight), granum (pl: grana; stacks of thylakoids), stroma (fluid inside the outer membrane, which interacts with the cytoplasm. It surrounds the granum and thylakoids

Mitochondrion plural: mitochondria

found in almost all cells

converts chemical energy (sugar) into another form of chemical energy (ATP), which is simpler and could be used by the cell

process is cellular respiration: composed of Glycolysis, ETC, and Oxidative Phosphorylation

has two compartments. Crista (pl:cristae) is the compartment formed by the inner and outer membrane of the mitochondria; it is the layer of folds in the mitochondria and is studded with proteins. The other compartment is called matrix; it is the fluid inside the foldings (cristae).

SECTION 3

Cell membrane consists of a double layer (bilayer) of phospholipids interspersed

with other molecules.

A phospholipid is a molecule composed of three parts

1. a charged phosphate group

2. glycerol

3. two fatty acid chains

the glycerol and the phosphate group form the head of a phospholipid

o polar because it forms a charge

o forms a hydrogen bond with water molecule (which is also polar)

the fatty acids form the tail

o non polar

o cannot form a hydrogen bond with water so the nonpolar tails are

attracted to each other and repelled by water

Phospholipid heads are attracted to water and each other where the phospholipid

tails retreat from water and pivot inward creating a bilayer.

Fluid Mosaic Model

The Fluid Mosaic Model states that membranes are composed of a Phospholipid

Bilayer with various protein molecules floating around within it. The cell

membrane is flexible. The 'Fluid' part represents how some parts of the membrane

can move around freely, if they are not attached to other parts of the cell. They

can move from side to side and slide past each other. The 'mosaic' part illustrates

the 'patchwork' of proteins that is found in the Phospholipid Bilayer.

The cell membrane has a property of selectively permeability (or semipermeable)

which means it allows some, but not all, materials to cross. It enables a cell to

maintain homeostasis in spite of unpredictable, changing conditions outside the

cell.

Example of selectively permeability is outdoor clothing. The material is

waterproof yet breathable. Water cannot get into the fabric but sweat can

get out because molecules are smaller.

Molecules cross the cell membrane in several ways. Some methods require energy

and some do not. Crossing the membrane depends on

Molecules size (smaller are easier to pass)

Polarity (nonpolar are easier to pass)

Concentration inside versus outside of the cell

SECTION 4

Passive transport is the movement of molecules across the cell membrane without

energy input from the cell

2 Types of passive transport

Diffusion

Osmosis

Diffusion is the movement of molecules in a fluid or gas from a region of higher

concentration to a region of lower concentration. This is the results from natural

motion of particles.

Example is dropping a drop of food coloring into a glass of water.

Concentration is the number of molecules of a substance in a given volume and

can vary from one region to another.

Concentration gradient is the difference in the concentration of a substance from

one location to another. Molecules diffuse down their concentration gradient,

which means they go from higher to lower concentration.

Osmosis is the movement across a semipermeable membrane from an area of

higher water concentration to an area of lower water concentration.

The area of higher concentration of dissolved particles in a solution, the

lower the concentration of water molecules in the same solution

Ex. A cup with 1 teaspoon of salt in a cup of water compared to a cup

with 10 teaspoons of salt in cup of water. There is more water in the

first cup.

A solution may be described as isotonic, hypotonic or hypertonic.

Isotonic – a solution with same concentration of solutes as the cell. Equal

amounts of water enter and exit the cell, so the cell stays constant.

Hypotonic – a solution has fewer solutes than a cell. More water enters the

cell causing the cell to expand or even burst (lysed).

Hypertonic – a solution has more solutes than a cell. More water exits a cell

causing the cell to shrivel or even die.

In plants the cell wall will help the cell from swelling to much which causes the

water to be forced into the central vacuole.

Facilitated diffusion is the diffusion of molecules across a membrane through

transport proteins.

Facilitate means to make easier

Transport proteins make it easier for molecules to enter or exit a cell but it is

still a form of passive transport because no energy is needed for this to

occur.

SECTION 5

Active transport moves molecules across a membrane from areas of lower

concentration to a region of higher concentration.

Because you are going from lower to higher energy is needed since its going

across the concentration gradient.

There are 2 types of active transport

1. Endocytosis

2. Exocytosis

Endocytosis is the process of taking liquids or fairly large molecules into a cell by

engulfing them in membrane.

Steps of endocytosis (import materials)

1. The cell membrane folds inward and fuses together surrounding the

substance in a pocket

2. The pocket pinches off inside the cell forming a vesicle

3. The vesicle fuses with a lysosome or similar vesicle where enzymes

break down the membrane and contents

Two types of endocytosis

1. Phagocytosis – cells engulf a particle or another cell and enclose it

within a sac

2. Pinocytosis – cells gulp up droplets of extracellular fluid and any solutes

that are dissolved in it.

Key difference: Pinocytosis is the absorption of liquids, whereas

phagocytosis is the absorption of solid objects which are essentially food

for the cell.

Exocytosis is the opposite of endocytosis. It is the release of substances out of a

cell by fusion of a vesicle with the membrane.

Steps of exocytosis (export materials)

1. The cell forms a vesicle around material that needs to be removed or

secreted

2. The vesicle is transported to the cell membrane

3. The vesicle membrane fuses with the cell membrane and releases the

contents

Top picture is endocytosis and the bottom picture is exocytosis