3.2.1..1 Structure of eukaryotic cells

What organisms are eukaryotic?

• Animals

• Plants

• Algal

• Fungal

What organelles do plant cells have that animal cells don’t?

• Cellulose wall with plasmodesmata (channels for exchanging substances between adjacent cells)

• Vacuole

• Chloroplasts

What organelles do plant and animal cells both have?

• Cell-surface plasma membrane

• Rough endoplasmic reticulum

• Lysosomes

• Ribosomes

• Nuclear envelope

• Golgi apparatus

• Cytoplasm

• Mitochondrion

• Nucleus

• Nucleolus

• Smooth endoplasmic reticulum

What are the difference between plant cells and algal cells?

• Algal cells can be either unicellular or multicellular

• The chloroplasts in many algal cells are a different shape and size to those in plant cells

• E.g. some algae have one large chloroplast rather than several smaller chloroplasts

What are the 2 differences between fungal and plant cells?

• Fungal cell walls are made of chitin, not cellulose

• Fungal cells do not have chloroplasts because they don’t photosynthesise

Cell-surface membrane - description

• The membrane found on the surface of animal cells and just inside the cell wall of other cells

• It is made mainly of lipids and proteins

Cell-surface membrane - function

It regulates the movement of substances into and out of the cell. It also has receptor molecules on it, which allow it to respond to chemicals like hormones

Nucleus - description

• A large organelle surrounded by a nuclear envelope (double membrane), which contains many pores

• It contains chromosomes and nucleolus

Nucleus - function

• It controls the cell’s activities (by controlling the transcription of DNA)

• DNA contains instructions to make proteins

• The pores allow substances to move between the nucleus and the cytoplasm

• The nucleolus makes ribosomes

Mitochondrion - description

• Usually oval shaped

• Double membrane- the inner one is folded to form structures called cristae

• Inside is the matrix, which contains enzymes involved in respiration

Mitochondrion - function

• The site of aerobic respiration

• Aerobic respiration produces ATP

• Mitochondria are found in large number of cells that are very active and require a lot of energy

Chloroplast - description

• A small, flattened structure found in plant cells and algal cells

• It is surrounded by a double membrane, and also has membranes inside called thylakoid membranes

• These membranes are stacked up in some parts of the chloroplast to form grana

• Grana are linked together by lamellae, which are thin, flat pieces of thylakoid membrane

Chloroplast - function

• The site where photosynthesis takes place

• Some parts of photosynthesis happen in the grana, and other parts happen in the stroma ( a thick fluid found in chloroplasts)

Golgi apparatus - description

• A group of fluid-filled membrane - bound flattened sacs

• Vesicles are often seen at the edges of the sacs

Golgi apparatus - function

• It processes and packages new lipids and proteins

• It also makes lysosomes

Golgi vesicle - description

A small fluid - filled sac in the cytoplasm, surrounded by a membrane and produced by the golgi apparatus

Golgi vesicle - function

It stores lipids and proteins made by the golgi apparatus and transports them out of the cell (via the cell-surface membrane)

Lysosome - description

• A round organelle surrounded by a membrane, with no clear internal structure

• It is a type of golgi vesicle

Lysosome - function

• It contains digestive enzymes called lysozymes

• These are kept separate from the cytoplasm by the surrounding membrane, and can be used to digest invading cells or to break down worn out components of the cell

Ribosome - description

• A very small organelle that floats free in the cytoplasm or is attached to the rough endoplasmic reticulum

• It is made up of proteins and RNA

• It is not surrounded by a membrane

Ribosome - function

The site where proteins are made

Rough endoplasmic reticulum (RER) - description

• A system of membranes enclosing a fluid-filled space

• The surface is covered with ribosomes

Rough endoplasmic reticulum (RER) - function

It folds and processes proteins that have been made at the ribosomes

Smooth endoplasmic reticulum (SER) - description

Similar to RER, but with no ribosomes

Smooth endoplasmic reticulum (SER) - function

It synthesises and processes lipids

Cell wall - description

• A rigid structure that surrounds cells in plants, algae and fungi

• In plants and algae it is made mainly of the carbohydrate cellulose

• In fungi, it is made of chitin

Cell wall - function

It supports cells and prevents them from changing shape

Cell vacuole (plants) - description

• A membrane-bound organelle found in the cytoplasm

• It contains cell-sap, which is a weak solution of sugars and salts

• The surrounding membrane is called the tonoplast

Cell vacuole (plants) - function

• It helps to maintain pressure inside the cell and keep the cell rigid

• This stops plants wilting

• It is also involved in the isolation of unwanted chemicals inside the cell