A Level Biology Mind Maps

Lesson Summary: Cell Structure

Cell structure is a fundamental topic in A Level Biology because all living organisms are made of cells. Understanding cell structure helps explain how living organisms function and provides a foundation for later topics such as infectious diseases, transport, respiration and photosynthesis.

This lesson introduces the differences between eukaryotic cells, prokaryotic cells and viruses. Eukaryotic cells, such as plant and animal cells, contain membrane-bound organelles. Prokaryotic cells, such as bacteria, are smaller and simpler, while viruses are non-cellular structures.

The Microscope in Cell Studies

Light microscopes are important tools used to observe cells and larger cell structures. Students need to know how to prepare temporary slides of cellular material for viewing. They should also be able to draw cells accurately from microscope slides and photomicrographs.

A key skill in this lesson is calculating magnification, image size and actual size using drawings, photomicrographs and electron micrographs. Students must also understand how to use an eyepiece graticule and a stage micrometer to make accurate measurements in millimetres, micrometres and nanometres.

The lesson also explains the difference between magnification and resolution. Magnification is how many times larger an image appears compared with the real object. Resolution is the ability to distinguish two close points as separate. Electron microscopes have a higher resolution than light microscopes, so they show more detail of cell ultrastructure.

Eukaryotic Cell Structures

Students must recognise and describe the structure and function of organelles found in eukaryotic cells. These include the cell surface membrane, nucleus, nuclear envelope, nucleolus, rough endoplasmic reticulum, smooth endoplasmic reticulum, Golgi body, mitochondria, ribosomes, lysosomes, centrioles, microtubules, cilia, microvilli, chloroplasts, cell wall, plasmodesmata, large permanent vacuole and tonoplast.

Plant and animal cells have many similarities, such as a cell surface membrane, cytoplasm, nucleus, mitochondria and ribosomes. However, plant cells also contain structures such as a cellulose cell wall, chloroplasts, plasmodesmata and a large permanent vacuole. These differences are linked to their functions, such as photosynthesis, support and storage.

Cells use ATP produced during respiration as an immediate energy source for energy-requiring processes.

Prokaryotic Cells

Prokaryotic cells, such as bacteria, are unicellular and are generally about 1–5 micrometres in diameter. They have peptidoglycan cell walls, circular DNA and 70S ribosomes. They do not contain organelles surrounded by double membranes, such as a nucleus, mitochondria or chloroplasts.

Students must be able to compare prokaryotic cells with typical eukaryotic plant and animal cells.

Viruses

Viruses are not cells. They are non-cellular structures made of a nucleic acid core, which may be DNA or RNA, surrounded by a protein coat called a capsid. Some viruses also have an outer envelope made of phospholipids.

Key Learning Focus

By the end of this lesson, students should be able to identify cell structures, describe their functions, compare plant, animal and bacterial cells, interpret micrographs and biological drawings, and understand how microscopy is used to study cells.