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Cell Organelles

An organelle is a small structure within the cell (organelle literally means 'tiny structure'). Some examples of cell organelles are cell wall, cell membrane, and nucleus.

The following are the major functions of organelles :
  • protection/support
  • barrier between cell and its environment
  • building and repairing of cell parts
  • transport of materials
  • storage and release of energy
  • disposal of waste materials
  • reproduction (increase in number)

Cell Wall

The cell wall is found in plant cells, but not in animal cells. This is the outermost layer in the plant cell. It is stiff, rigid, nonliving, and made of cellulose. It provides support so that the plant can grow tall and protection. Some materials like water, oxygen, and carbon dioxide can pass through it.

Cell Membrane

The cell membrane is found in both plant and animal cells. It is the outermost layer in the animal cell and is found just inside the cell wall in the plant cell. The animal cell membrane contains cholesterol, but the plant cell does not. It has pores and is selectively permeable allowing the movement of certain substances into and out of the cell. This helps maintain homeostasis in the cell. The cell membrane also protects and supports the cell.


The nucleus is a large, oval structure found in both plant and animal cells. It controls and regulates all cell activities. It contains the genetic material.

Nuclear Membrane

The nuclear envelope (perinuclear envelope, nuclear membrane, nucleolemma, karyotheca) is a double lipid bilayer that encloses the genetic material in eukaryotic cells. The nuclear envelope also serves as the physical barrier, separating the contents of the nucleus (DNA in particular) from the cytosol (cytoplasm).

Numerous nuclear pores are inserted in the nuclear envelope and facilitate and regulate the exchange of materials (proteins such as transcription factors, and RNA) between the nucleus and the cytoplasm).


The cytoplasm is a thick, jellylike substance found in both plant and animal cells filling the space between the nucleus and the cell membrane. It contains and supports the cell organelles. The cytoplasm is constantly in motion.

Endoplasmic Reticulum (E.R.)

The endoplasmic reticulum (ER) is responsible for the production of the protein and lipid components of most of the cell's organelles. The ER contains a great amount of folds - but the membrane forms a single sheet enclosing a single closed sac. This internal space is called the ER lumen. The ER is additionally responsible for moving proteins and other carbohydrates to the Golgi apparatus, to the plasma membrane, to the lysosomes, or wherever else needed.

There are two types of ER - rough, which is coated with ribosomes, and smooth, which isn't. Rough ER is the site of protein synthesis. The smooth ER is where the vesicles carrying newly synthesized proteins (from the rough ER) are budded off and are devoid of ribosomes .


The ribosome is plays a key role is the synthesis of protein. When the polypeptide chain is growing it must be kept aligned with the mRNA molecule so that each codon still hooks up with the tRNA molecule. After the addition of one amino acid the chain is moved down three codons. This is done using a large complex composed of protein and RNA, called the ribosome.

Ribosomes consist of one large unit and one small unit. Half of the eukaryotic ribosomal weight comes from RNA. The ribosome contains a groove that guides the polypeptide chain and another groove that holds the mRNA molecule.



The mitochondrion is a bean-shaped structure found in both plant and animal cells. The mitochondria (plural) break down sugars and release energy for use by the cell and are hence known as the 'power house' of a cell . It has inner membrane folds called cristae. Cells with high activity levels contain more mitochondria, such as muscle cells.


The vacuole is a round, fluid-filled sac found in both plant and animal cells. Plants usually have a few large vacuoles, while animal cells have smaller vacuoles, if any. It stores food, water, and other materials for use by the cell. Wastes may also be stored in vacuoles . The membrane that lines the vacuoles in plants is called tonoplast.


The lysosome is a small, round structure common in animal cells, but not usually found in plant cells. The lysosome is involved in digestive activities, including breaking down large food molecules into smaller ones and the digestion of old cell parts.


A chloroplast is found in plant cells, but not in animal cells. Chloroplasts are oval-shaped, green structures having an outer and an inner membrane, a matrix or stroma containing grana made up of thylakoids containing chlorophyll, a green pigment. They use the sun's energy to make food for the plant through a process called photosynthesis. The photograph below was taken of Elodea, a water plant. All of the darker spots in the cell are chloroplasts!





Cell wall

Plant, not Animal

*outer layer

*rigid, strong, stiff

*made of cellulose

*support (grow tall)


*allows H2O, O2, CO2 to pass into and out of cell

Cell membrane

both Plant/Animal

*Plant - inside cell wall

*Animal - outer layer; cholesterol

*selectively permeable



*controls movement of materials in/out of cell

*barrier between cell and its environment

*maintains homeostasis


both Plant/Animal

*large, oval

*controls cell activities

Nuclear Membrane

both Plant/Animal

*surrounds nucleus

*selectively permeable

*Controls movement of materials in/out of nucleus


both plant/animal

*clear, thick, jellylike material and organelles found inside cell membrane

*supports /protects cell organelles

Reticulum (E.R.)

both Plant/Animal

*network of tubes or membranes

*carries materials through cell


both Plant/Animal

*small bodies free or attached to E.R.

*produces proteins


both Plant/Animal

*bean-shaped with inner membranes

*breaks down sugar molecules into energy


Plant - few/large
Animal - small

*fluid-filled sacs

*store food, water, waste (plants need to store large amounts of food)


Plant - uncommon
Animal - common

*small, round, with a membrane

*breaks down larger food molecules into smaller molecules

*digests old cell parts


Plant, not Animal

*green, oval usually containing chlorophyll (green pigment)

*uses energy from sun to make food for the plant (photosynthesis)

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