2.1.1 Cell Structure

flagellum

flagellum

flagella on eukaryotic cells are like cilia but longer. they stick out from the cell surface and are surrounded by the plasma membrane

inside they have two microtubules in the centre and nine pairs around the edge

→the microtubules contract to make the flagellum move. this movement propels cells forwards

chloroplasts

a small, flattened structure found in plant cells. it is surrounded by a double membrane, and also has membranes inside called thylakoid membrane

these membranes are stacked up in some parts of the chloroplast to form grana. grana are linked together by lamella- thin, flat pieces of thylakoid membrane

→the site of photosynthesis. some parts happen in the grana and others in the stroma (a thick fluid)

centriole

small, hollow cylinders, made of microtubules. found in animal cells, but only some plant cells

→involved in the separation of chromosomes during cell division

golgi appartus

a group of fluid-filled, membrane-bound, flattened sacs. vesicles are often seen at the edge

→it processes and packages new lipids and proteins and makes lysosomes

ribosome

a very small organelle that either floats free in the cytoplasm or is attached to RER. it is made up of proteins and RNA. it is not surrounded by a membrane

→the site where proteins are made

plasma membrane

the membrane found on the surface of animal cells and just inside the cell wall of plant cells. it is made mainly of lipids and proteins

→regulates the movement of substances into and out of the cell. it also has receptor molecules on it, which allows it to respond

cell wall

rigid structure that surrounds plant cells. it is made mainly of the carbohydrate cellulose

→supports plant cells

mitochondrion

it’s usually oval-shaped. it has a double membrane- the inner one is folded to form structures called cristae

inside is the matrix, which contains enzymes involved in respiration

→the site of aerobic respiration, where ATP is produced. mitochondria are found in large number in cells that are very active

cilia

hair-like structures found on the surface membrane of some animal cells. in cross-section, they have an outer membrane and a ring of nine pairs of protein microtubules inside, with a single pair of microtubules in the middle

→the microtubules allow the cilia to move. this movement is used by the cell to move substances along the cell surface

nucleus

a large organelle surrounded by a nuclear envelope (double membrane), which contains many pores. the nucleus contains chromatin- DNA and proteins. it also contains the structure called the nucleolus

→the nucleus controls the cell’s activities. the DNA contains instructions to make proteins. the pores allow substances to move between the nucleus and the cytoplasm. the nucleolus makes ribosomes

rough endoplasmic reticulum

a system of membranes enclosing a fluid-filled space. the surface is covered with ribosomes

→folds and processes proteins that has been made at the ribosomes

smooth endoplasmic reticulum

a system of membranes enclosing a fluid-filled space with no ribosomes

→synthesises and processes lipids

lysosomes

a round organelle surround by a membrane, with no clear internal structure

→contains digestive enzymes. these are kept separated from the cytoplasm and are used to digest invading cells or break down worn out components of the cell