Eukaryotic Cells and Their Organelles
Eukaryotic cells contain a nucleus and membrane-bound organelles. All multicellular organisms consist
of eukaryotic cells. Eukaryotic cells are thought to have evolved from primitive single-celled prokaryotic cells.
All cells are surrounded by a cell membrane (plasma membrane). The cell membrane is
semipermeable, allowing some substances to pass into the cell and blocking others. It is composed of a
double layer of phospholipids and embedded proteins.
Plant cells have an additional layer surrounding them called the cell wall. The cell wall is made of
nonliving material called cellulose.
The centrosome (also called the "microtubule organizing center") is a small body located near the
nucleus. The centrosome is where microtubules are made. During cell division (mitosis), the centrosome
divides and the two parts move to opposite sides of the dividing cell. The centriole is the dense center of the
centrosome. Only animal cells have centrosomes. Microtubules are shaped like soda straws and give the
nucleus and cell its shape.
The nucleus in the center of a cell is a spherical body containing the nucleolus that makes ribosomes.
The nucleus controls many of the functions of the cell (by controlling protein synthesis). It also contains DNA
assembled into chromosomes. The nucleus is surrounded by the nuclear membrane. Materials can move
from the nucleus to the cytoplasm through nuclear pores in the membrane around the nucleus.
Cytoplasm is the jellylike material outside the cell nucleus in which the organelles are located.
All cells, even prokaryotes contain small bodies called ribosomes. Proteins are made here by a
process called protein synthesis.
Rough endoplasmic reticulum (rough ER) is a vast system of interconnected, membranous, infolded
and convoluted sacks that are located in the cell's cytoplasm. The ER is continuous with the outer nuclear
membrane. Rough ER is covered with ribosomes that give it a rough appearance. Rough ER transports
materials through the cell and produces proteins in sacks called cistern which are sent to the Golgi body, or
inserted into the cell membrane. The Golgi apparatus or Golgi complex is a flattened, layered, sac-like
organelle that looks like a stack of pancakes. The Golgi body modifies & packages proteins and carbohydrates
into membrane-bound vesicles for "export" from the cell. Smooth ER does NOT have ribosomes on its
surface. It makes proteins and lipids that will be exported by the cell. It also controls the calcium level in
muscles and detoxifies poisons, alcohol, and drugs.
Only plant cells, not animal cells, can make their own food in a plant-only organelles called a
chloroplast. Chloroplasts are elongated or disc-shaped organelles containing chlorophyll that trap sunlight for
energy. Photosynthesis (in which energy from sunlight is converted into chemical energy - food) takes place in
the chloroplasts. Plant cells also contain fluid-filled sacs called vacuoles. The vacuole fills with food being
digested and waste material that is on its way out of the cell. In plant cells, a large central vacuole takes up
most of the space in the cell.
Mitochondria are spherical to rod-shaped organelles with a double membrane. The inner membrane is
infolded many times, forming a series of projections called cristae. The mitochondrion converts the energy
stored in glucose into ATP (adenosine triphosphate) for the cell. In plant and animal cells the mitochondria
have double membranes and their own DNA.
Cells also contain spherical organelles called lysosomes that contain digestive enzymes. Nutrients are
digested by the cell here, as well as, old cell organelles that are going to be recycled.
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1 What do eukaryotic cells have that makes them eukaryotic?
2 What surrounds all cells?
3 What is meant by semipermeable?
4 What 2 things make up the cell membrane?
5 The cell membrane is also called the ____________ membrane.
6 Centrioles are found inside of what type of cell? _______________
7 What additional layer is found around the outside of plant cells and bacteria?
8 Centrioles are found at the center of the _________________. How do they help the cell?
9 Where is DNA found inside a cell?
10 DNA coils tightly during division and assembles into visible _________________.
11 Where are organelles located?
12 Where are proteins made in a cell?
13 Do all cells need ribosomes? ____________
14 The process of making proteins is called ________________________.
15 How does rough ER differ from smooth ER?
16 Rough ER is connected to the _____________ membrane and to __________ER.
17 Proteins made by rough ER travel to the Golgi in sacks called _____________.
18 The Golgi body ____________ and ___________ proteins for export out of the cell.
19 Give 3 jobs for smooth ER.
1) _________________________
2)________________________
3)_____________________
20 Chloroplasts are found in what type of cell(s)? __________________
21 What process takes place inside chloroplasts? ______________What is the energy used for this
process?________________ What gas is taken out of the atmosphere? _____________________
22 What pigment traps the energy? _____________
23 Both chloroplasts and mitochondria are alike in that they both have _________________ membranes
and their own ___________.
24 Food, water, and wastes are stored inside ______________.
25 Digestion takes place inside _____________ containing _____________.
26 The largest organelle in plants is the ____________ _____________.
27 What organelle breaks down and recycles worn out cells? _________________________.
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Figure 2 – Plant Cell
Figure 1 - Animal Cell
On the two cells color the organelles as follows:
Mitochondria – orange
Nucleus – blue
Cell membrane - yellow
Cell Wall – purple
Rough ER – violet
Smooth ER – brown
Golgi apparatus – any color
Centrioles – any color
Cytoplasm- white
ANIMAL CELL
Cholorplasts – green
Large Vacuole – red
Ribosomes - black
Cilia - yellow
PLANT CELL
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Prokaryotic Cells – Bacteria
Prokaryotes cells are the simplest of all the cells. Unlike eukaryotes, they do not have a nucleus to hold
their DNA so their DNA strand is floating freely in the cell. They also do not have membrane-bound organelles
and prokaryotic organisms are always single-celled. The best examples of prokaryotes are bacteria.
Bacteria are prokaryotes and they fall into two major categories: The Kingdom Eubacteria and the
Kingdom Archaebacteria. Eubacteria are common types that occur all around us, usually in they are, on
surfaces and in the soil. You can only find Archaebacteria in extreme environments, like hot sulfur springs.
Archaebacteria are thought to be some of the oldest life forms on earth.
Most bacteria don't make their own food. That means they have to rely on other organisms to provide
them with food. These bacteria have to break down, or decompose, other living things to obtain energy.
When most people hear the word bacteria, they think of something that is bad for you. In fact, very few
bacteria cause illness. Some bacteria actually help you! Bacteria are used to make food, such as cheese and
yogurt, and they can also help us break down harmful substances in the environment. Scientists created a type
of bacteria that could gobble up oil from oil spills. Some bacteria live inside the guts of animals and help them
to digest food.
Unfortunately, there are many types of bacteria that can make us ill. Salmonella bacteria can cause
food poisoning, and certain types of bacteria are responsible for other infections. You might have had some
experience with Streptococcus pyogenes, the bacteria that causes strep throat.
Bacteria have a very simple cell design. Most of them have a thick outer covering called the cell wall.
Just within the cell wall is the cell membrane.
Along the surface of the bacteria cell, you might encounter structures called pilus, whose job is to help
the bacteria stick to surfaces. Bacteria might also need to move around in their environment, so they can have
structures called flagella, which resemble tails.
The watery interior of the cell is called cytoplasm, and it has the texture of jello. Sprinkled throughout
the cell are small roundish structures called ribosomes. Ribosomes make proteins for the cell.
Every prokaryote cell has DNA floating within the cytoplasm, which usually looks like a twisted strand of
spaghetti. DNA contains the instructions for the cell, basically it is the control center.
On the cell color the structures as follows: DNA – blue,
Cell membrane – yellow, Cell Wall – purple, Ribosomes –
black, Pilus/Cilia – green, Cytoplasm – white, Flagella – red
1. What don’t prokaryotes have that eukaryotes do?
2. What thought to be the oldest life forms?
3. What type of environments do Archaebacteria live
in?
3. What two foods does bacteria help us make?
4. To what kingdom do common bacteria belong to?
5. How do bacteria move around?
6. Where are proteins made in bacteria?
7. Bacteria have a cell wall. What type of eukaryotic cell also has a cell wall? __________________
8. How many cells can a bacteria have? ____
9. Another term for pili is ________.
10. Do bacteria have DNA? ____ What about a nucleus? _____
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