2 Structure and functionof cells

Looking at cells

The plasma membrane boundary

Figure 2.4 The fluid mosaic model proposed by Singer and Nicholson for the structure of the plasma membrane of a red blood cell. The lipid in the membrane is a complex lipid known as phospholipid. What does this name suggest about this lipid? The carbohydrate groups in the outer surface form part of antigens (see chapter 3).

The plasma membrane forms the boundary of each living cell. It is selectively permeable.

Several different processes* exist whereby substances may cross plasma membranes.

*( 2x diffusion, osmosis, active transport and bulk transport)

Cell walls lie outside the plasma membrane of plant, fungal and prokaryotic cells.

The plasma membrane

Prokaryotic cells lack any internal membrane-bound organelles.

In eukaryotic cells, the nucleic acid DNA is enclosed within the nucleus, a double-membrane-bound organelle.

Living cells use energy all the time, principally as chemical energy present in ATP.

Mitochondria are the major sites of ATP production in eukaryotic cells.

Cell organelles

Ribosomes are tiny organelles where proteins are produced.

The endoplasmic reticulum (ER) is a series of membrane-bound channels, continuous with the membrane of the outer nuclear envelope, that transport substances within a cell.

The Golgi complex packages substances into vesicles for export.

Cell organelles

Lysosomes can digest material brought into their sacs. Lysosomes play a role in organised cell death.

Chloroplasts are relatively large organelles found in photosynthetic cells of plants and algae.

Chloroplasts have an external membrane and layers of folded internal membranes and contain pigments called chlorophylls.

Other important organelles…

Chloroplasts can capture the radiant energy of sunlight and convert it to chemical energy in sugars.

Structures known as flagella are present on many prokaryotic cells.

Cilia or flagella are present on many eukaryotic cells.

Flagella and cilia are cell organelles associated with movement.

Other important organelles…

Lysosome

Golgi Apparatus

Single-celled organisms are able to carry out all the metabolic processes necessary for life.

In multicellular organisms, cells become differentiated to perform specialised functions.

The different levels of organisation of cells in multicellular organisms are single cell, tissues, organs, systems and the whole organism.

Individual cells in a group of cells must be able to receive an adequate supply of materials and get rid of wastes.

Each system serves the needs of other systems.

Cells in multicellular organisms:levels of organisation