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Cell Biology

Cell Biology is the first unit which we will be covering in Higher Biology.

It will cover a wide variety of topics including;

• Cell Structure in Relation to Function
• Photosynthesis
• Energy Release (Respiration)
• Synthesis and Release of Proteins
• Cellular Response in Defence in Animals and Plants

Every second week you should expect to be allocated homework and have a multiple choice quiz to do in class time. Aim to keep on top of this as it gives an indication of how you will cope with end of unit NABs and the final exam.

Cell Structure in Relation to Function

This week in Higher Biology we have been learning about the main organelles which make up a plant and animal cell.

The new organelles we met were;

rough endoplasmic reticulum – transports newly made proteins.

ribosomes – the site of protein synthesis

mitochondrion – the site of aerobic respiration.

Golgi apparatus – processes and packages the newly made proteins before they are secreted from the cell.

Lysosomes – contains digestive enzymes to break down invading microbes.

The video below summarises the main structures we have been learning about.

Unicellular and Multicellular Organisms

Unicellular organisms are organisms made of a single cell.

We have also been learning about how cells form tissues within multicellular organisms like humans. Each cell within a tissue has a structure which is suited to it’s function.

Nerve cells are long  and make many connections with other nerves.

Goblet cells are cup-shaped and produce mucus in the trachea. Many golgi apparatus help to process and package the proteins in the mucus.

Palisade mesophyll cells contain many chloroplasts since they are the main site of photosynthesis.

Root hair cells have long extensions which provide it with a large surface area for absorption.

Cell Membrane

This week we have been learning about the structure of the cell membrane and cell wall. Here are some of the class’s efforts.

Cell Membrane Model

Cell Wall Model 

Good effort overall. Remember the phospholipids and proteins which work together to make the cell membrane. Hydrophilic phosphate heads and hydrophobic lipid tails, together make the phospholipids.The cell membrane is often described as a fluid mosaic. Fluid because of the constant movement of the phospholipids and mosaic because of the large and small parts of the membrane which are arranged randomly.The cell membrane is arranged as a bilayer of phospholipids with proteins interspersed throughout. It is selectively permeable, allowing some molecules such as oxygen and water to pass through. The cell wall is fully permeable and made of cellulose fibres which are slightly elastic.

The Structure of the Cell Membrane Experiment

Later in the week the class carried out an experiment to investigate the chemical structure of the cell membrane. The pupils used some red cabbage and placed them in water at 25°C, water at 70°C, alcohol and acid. The extent of bleeding in each of the test tubes was measured using a calorimeter. The lovely results are demonstrated below;

The high temperature denatured the proteins in the cell membrane allowing a high level of bleeding. The acid and alcohol disrupt the lipid part of the cell membrane also allowing bleeding to take place.

The proteins in the cell membrane perform a number of different roles such as

– enzymes

– providing structural support.

– receptors

– as an antigenic marker

– as a carrier

and a variety of other roles.

Cell Transport – Diffusion

Diffusion involves the movement of substances from an area of high concentration to an area of low concentration through a selectively permeable membrane. This is the movement of molecules down a concentration gradient.

For very small molecules, such as oxygen and carbon dioxide this can take place through the phospholipid part of the cell membrane.

Facilitated diffusion – this is a form of diffusion which enables slightly larger molecules such as glucose to move across the

membrane. This requires the help of a protein to take place.

These processes DO NOT require energy.

Here is a table to summarise diffusion;

Substance Movement through the membrane
WaterOxygenCarbon dioxide Tiny molecules, rapid diffusion across the phospholipid bilayer
Urea Diffusion across phospholipid bilayer but slower than water
GlucoseAmino acidsCharged particles (ie K+) Do not diffuse through bilayer, Require membrane channel proteins and carrier proteins for slow diffusion
StarchProtein Unable to diffuse through the membrane (too large)

Cell Transport – Osmosis

Osmosis involves the movement of substances from an area of high water concentration to an area of low water concentration through a selectively permeable membrane. This is the movement of molecules down a concentration gradient.

Three words are often used to describe the internal conditions of a cell or the surrounding solutions. These are hypertonic, isotonic and hypotonic.

Hypertonic = less water

Hypotonic = more water

Isotonic = equal water concentration.

Both osmosis and diffusion are forms of passive transport. They do not require energy.

Download the following sheets and complete them as revision. Draw diagrams showing what each cell should look like along with a description of the cell. Also label which solution is hypotonic, isotonic and hypertonic.      Osmosis Revision

Cell Transport – Active Transport

Active Transport – The movement of molecules and ions across the plasma membrane from a

low to a high concentration (against a concentration gradient)

–       This process requires energy (ATP).

–       This energy comes from respiration.

Factors such as temperature, availability of oxygen and concentration or respiratory substrate (eg. Glucose) which affect the cells respiration rate also affect active transport.

Make sure you feel comfortable both describing and explaining these graphs.

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