Cells

What is Life?

• Before we tackle this question, it is important to consider what qualifies something as “living”

Characteristics of Living Things • Cellular organization

• Growth and development

• Require energy to survive

• Cells have DNA

• Reproduction- all living things reproduce

• Sense and respond to change in environment

Living things include animals, plants, protists, fungi and bacteria

Homeostasis

• An organism’s outside environment may change, but conditions inside its body must remain the same

• Many chemical reactions keep an organism alive

• These reactions can only take place when conditions are exactly right

• An organism’s ability to maintain a stable, internal condition to survive is called homeostasis

• Homeostasis is the maintenance of a stable internal environment

• For example:

• Your body maintains a temperature of about 37 degrees Celsius

• When you get hot, your body responds by sweating

• When you are cold, your muscles twitch in an attempt to warm you up

• Some living things maintain homeostasis by changing their environment

• A tissue is a group of cells that work together to perform a certain job

Ex: blood, muscle, bone, fat, nerves

• An organ is a structure that is made of two or more tissues working together to perform a specific function

Ex: liver, heart, kidneys, lungs, brain

• An organ system is a group of organs working together to perform a certain job

Examples: circulatory system, digestive system, nervous system

Robert Hooke• In 1665, Hooke, a

physicist and inventor, became the first person to view cells using a slice of cork under a microscope

• He named what he saw cells because they reminded him of tiny rooms in a monastery

Anton van Leeuwenhoek1632-1723

• First scientist to view living cells

• Using a compound microscope that he invented, he discovered one-celled protists in pond water samples which he named animacules (little animals)

• He also saw bacteria (1676) from teeth scrapings, as well as sperm from dogs and other animals (1677)

The Cell Theory

A. All cells come from pre-existing cells

B. All organisms are either unicellular or

multi-cellular

C. Cells are the basic unit of structure of life

What are some benefits to being multicellular?

Unicellular

• An organism made up of one cell (bacteria and some protists)

Multicellular

• Organisms that are composed of many cells

(animals, plants, fungi, and some protsists)

Benefits to being multi-cellular

• Larger size

• Longer Life

• Specialization- each type of cell has a different job, making multi-cellular organisms more efficient than unicellular organisms

Five similarities of all Cells

• Require energy

• Produce proteins

• Have a cell membrane

• All cells divide to make new cells

• All have DNA (genetic material)

Eukaryotes Prokaryotes

• These are plant and animal cells

• These cells have enclosed membrane- bound organelles that carry out specific functions in the cell

• Multi-cellular• DNA is stored in a

nucleus

• These are bacterial cells

• Do not have membrane-bound organelles

• Unicellular • Lacks a nucleus;

instead it has a circular DNA region

Prokaryote

Prokaryotes are bacteria

They are unicellular organisms

They lack a nucleus,

Instead, the DNA is coiled as a long, circular strand in the center of the cell

Some bacteria have a flagellum that provides them with movement

Biological Molecules Our Body is Built on

• Carbohydrates (glucose)

• Lipids (fats)

• Proteins

• Nucleic Acid

Cells rely on these to do their job, and in the cell you will soon learn that proteins and lipids are even manufactured there!

Organelles

• Tiny cell structures that carry out specific jobs

• They are membrane-bound

• Found in both plant and animal cells (eukaryotes), but not in bacterial cells

As you will soon see, the cell is like a factory- different organelles working together

to make important materials for the cell

The cell membrane is semi-permeable (only some things pass through it)- it controls what goes in and out of the

cell-allows certain molecules to pass through

Nucleus

• The “control center” of the cell, because it contains DNA, it directs all the cell’s activities

• The nucleus is protected and surrounded by a nuclear membrane

Stores DNA….It is the control center of the cell!!

Nucleolus

• This small structure is located inside the nucleus

• It is the site for the production of ribosomes

Ribosomes

• Attached to the surface of some endoplasmic reticulum, but also free floating in the cytoplasm

• Makes (synthesizes) proteins

• Proteins are made here and then sent to the golgi bodies via vesicles

• Proteins are responsible for thousands of different chemical reactions that keep us alive and are also responsible for traits we are born with , like eye color and lip shape, etc

The Protein Factories!

ChromatinChromatin are very thin strands of genetic material (DNA) that float around in the nucleus (the purple lines)

These strands are the reason the nucleus is the “control center” of the cell

Lysosomes

Small round structures that contain chemicals that break down large food parts and old, worn-out cell materials

They also release enzymes, so that they may be used again

More common in animal cells than plant cells

MitochondriaRod shaped structures with a double- layer membrane

The “power houses” of the cell because they produce energy the cell needs to do its work

Unlike other organelles, they have their own DNA so they can divide and make more of themselves in the cell! Pretty cool, huh?

Energy Center of the Cell! Uses energy released from glucose molecules

Mitochondria• You eat and the

intestines break down food into small molecules

• A cell eats and the mitochondria breaks down the molecules for the cell using oxygen and glucose from food.

Structure of the Mitochondria

• In which type of cells would you expect to find a lot of mitochondria?

Muscle cells contain many mitochondria because our muscles require lots of energy to perform the tasks they do.

Cytoplasm

• The cytoplasm is the clear, gel-like fluid that is inside the cells between the cell membrane and the nucleus

• It is constantly moving

The jelly-like fluid in the cell that the organelles sit in is the cytoplasm

Endoplasmic Reticulum

A passageway through which proteins and other materials move within the cell

Spots on the endoplasmic reticulum are called ribosomes

Rough E.R. (has ribosomes)- so it makes proteins

Smooth E.R.-(lacks ribosomes) it makes lipids

The E.R. is always next to the nucleus

Rough Endoplasmic Reticulum

Proteins are transported by vesicles that bud off the E.R. and are sent to the golgi body and from the golgi body they

bud off and are sent to other parts of the cell

Golgi Bodies (Golgi Complex)

• Structures within the cell that look like a flattened stack of pancakes

• This structure is like the “post office”

• It sorts, packages, modifies proteins and other material, then distributes throughout the cell and out

Golgi Body

Plant cells have mostly the same organelles as animal cells, but a few differences do exist..

Plant Cell Wall

Cell Wall

• Found only in plant cells and bacterial cells

• It forms the outer most layer of the cell

• It protects and supports the plant cell

• It is rigid and made up of a carbohydrate called cellulose

The Outer Most Layer of a Plant Cell is the Cell Wall

All cells have a cell membrane!!!

• In animal cells, the cell membrane forms the outer layer• In plant and prokaryote cells, the cell wall forms the outer

most layer and the cell membrane is just inside of it• Animal Cell Plant Cell

Chloroplasts

• Large green structures found only in plant cells

• Chloroplasts capture energy from sunlight and use it to make food for the plant cell

• Chlorophyll in the chloroplasts are responsible for the plant’s green color and is the main pigment used in photosynthesis

Photosynthesis takes place in the stack of thylakoids

Central (large) VacuolesA sac like structure found in plant cells

Storage area-stores food and other important materials

When the vacuole is full of water the plant is plump and healthy

Without much water, the plant wilts because the vacuole shrivels, no longer supporting the cell wall

Similarities Among Cells

• All cells require energy to survive

• All cells make proteins (even prokaryotes)

• All cells have a cell membrane

• All cells contain DNA

• All cells come from a pre-existing cell

Warm-up

1. What three structures are only found in the plant cell?

2. What is the function of the nucleus? Of the mitochondria?

Prokaryote cells

• Prokaryote cells are bacteria cells

Cell Comparison

Eukaryote cell

• More modern cell• Contains DNA in an

enclosed organelle called a nucleus

• Has membrane- bound organelles

• Larger than prokaryotes

Prokaryote cell

• The earliest and simplest cells on earth

• Does not contain a nucleus; DNA floats freely in the cytoplasm

• Lacks organelles• Smaller than eukaryotes

Microscopes• Until the 1500’s, there was no way to see

cells. The first microscope was invented in 1590

• An instrument that makes small objects look larger

• A simple microscope uses only one lens, an example is a hand lens

• A compound microscope uses more than one lens (curved lenses) to focus light and can magnify an object up to 1000 times its size

Light Microscopes

• Works by magnifying an object by bending the light that passes through the curved convex lens

• The light passing through the lens bends inward, when this light hits the eye, the eye sees the object as larger than it really is

Electron Microscopes

• These microscopes send a beam of electrons over the surface of a specimen, rather than through it

• This results in a detailed, three- dimensional image of the specimen’s surface

• Electron microscopes can magnify an object up to 150,000 times its size!

The plasma membrane is made up of a phospholipid bilayer embedded with proteins

• The heads of the phospholipids are hydrophilic (water loving) and the tails facing inward are hydrophobic (water fearing)

• The lipid bilayer is called a fluid mosaic model because it has a fluid consistency comparable to light oil

One way that molecules pass through the cell membrane is by diffusion, a method of transfer that is passive and does not require energy. In the picture- water is the solvent and

the green substance is the solute

Facilitated Transport

Active Transport

Photosynthesis

Cellular Respiration