This page focuses on the structure of the cell membrane and the various mechanisms of transport across it. It provides detailed information on transport across cell membrane PDF content.

Definition: Cell membrane - Made of phospholipids and proteins, it is selectively permeable, allowing only certain molecules to pass through.

The page covers three main transport processes:

1. Diffusion: The movement of molecules from an area of high concentration to low concentration, requiring no energy.
2. Osmosis: The movement of water molecules through a selectively permeable membrane from an area of high water concentration to low water concentration.
3. Active Transport: The movement of molecules against a concentration gradient, from low to high concentration, requiring energy.

Example: In red blood cells, when placed in different water concentrations:

• High water concentration outside: Cell bursts
• Equal water concentration: No change in cell
• Low water concentration outside: Cell shrinks

The page also compares the effects of these transport mechanisms on plant cells, highlighting the role of the cell wall in preventing bursting and the phenomenon of plasmolysis.

Highlight: Understanding the differences between diffusion, osmosis, and active transport is crucial for National 5 Biology transport across cell membrane questions.

This page delves into the structure of DNA and the process of protein production, which is essential knowledge for National 5 Biology cell structure understanding.

Definition: DNA $Deoxyribonucleic Acid$ - Carries genetic information to make proteins, has a double-stranded helix structure with complementary base pairs.

The page outlines the steps in protein production:

1. Messenger RNA $mRNA$ copies the DNA code in the nucleus.
2. mRNA travels to a ribosome in the cytoplasm.
3. The ribosome uses the code to arrange amino acids in the correct order.

Vocabulary: Base pairs in DNA - Adenine $A$, Thymine $T$, Cytosine $C$, and Guanine $G$.

The page also covers the various functions of proteins, including structural roles, hormones, antibodies, receptors, and enzymes.

Highlight: Amino acids determine the structure and function of proteins, which is crucial for understanding cell membrane function in national 5 biology pdf.

The second half of the page focuses on enzymes:

Definition: Enzymes - Proteins that act as catalysts to speed up chemical reactions.

The page explains the lock-and-key model of enzyme action, where the substrate binds to the enzyme's active site. It also covers two types of enzyme-controlled reactions: synthesis $building larger molecules$ and degradation $breaking down larger molecules$.

This page continues the discussion on enzymes, focusing on their optimal conditions and factors affecting their activity. This information is crucial for understanding cell membrane function bbc Bitesize content.

Definition: Optimum conditions - The ideal circumstances under which enzymes function most effectively.

The page covers two main factors affecting enzyme activity:

1. Temperature: At optimum temperature, enzyme activity peaks. Beyond the optimum temperature, enzymes become denatured, lowering the reaction rate.
2. pH: Slight changes in pH can alter the active site of the enzyme. Significant pH changes can stop the enzyme from working altogether.

Highlight: Understanding how temperature and pH affect enzyme activity is essential for National 5 Biology units on cellular processes.

The page includes diagrams illustrating how enzymes become denatured at high temperatures, changing their shape and rendering them ineffective.

Example: When an enzyme is denatured, its active site changes shape, preventing it from binding with the substrate and catalyzing the reaction.

This information is particularly relevant for questions related to cell membrane structure and function in National 5 Biology exams.

This page introduces the concept of genetic engineering, which is the artificial transfer of genes from one organism to another. This topic is often covered in National 5 Biology Unit 2 summary notes.

Definition: Genetic Engineering - The process of artificially transferring genes from one organism to another to modify traits or introduce new characteristics.

The page outlines the stages of genetic engineering:

1. Identify the required gene section in the source DNA.
2. Extract the required gene using enzymes.
3. Extract a plasmid from a bacterial cell.
4. Cut open the plasmid using enzymes.
5. Insert and seal the required gene into the bacterial plasmid using an enzyme.

Example: Applications of genetic engineering in food production include:

• Golden Rice $enhanced with Beta Carotene$
• Blight-resistant potatoes
• Longer shelf-life tomatoes

Highlight: Genetic engineering is used to improve crops' nutritional quality, disease resistance, and shelf life.

The page emphasizes that these modified crops are examples of genetically modified organisms $GMOs$, which is an important concept in modern biology and often featured in Nat 5 Biology past papers.

This page covers the process of fermentation, which occurs in the absence of oxygen. Understanding fermentation is crucial for National 5 Biology Unit 3 Summary Notes.

Definition: Fermentation - A process that takes place when there is no oxygen present, allowing organisms to produce some energy from glucose.

The page compares fermentation in animal and plant cells:

1. In animal cells: Glucose is broken down into pyruvate and then lactate. This process occurs in the cytoplasm.
2. In plant cells $and yeast$: Glucose is broken down into pyruvate, which is then converted to ethanol and carbon dioxide. This also occurs in the cytoplasm.

Highlight: Fermentation produces less energy $2 ATP$ compared to aerobic respiration, but it allows for some energy production in anaerobic conditions.

The page also introduces the concept of a respirometer, used to measure the rate of respiration:

Example: In a respirometer, as a simple organism respires, oxygen is used up, causing the liquid in the tube to move as the volume decreases.

This information is particularly relevant for questions related to cell membrane function in national 5 biology pdf and cellular respiration processes.

This final page introduces the concept of respiration, which is the process by which cells release energy from glucose. This topic is crucial for understanding National 5 Biology units on cellular energy production.

Definition: Respiration - The chemical process by which energy stored in glucose is released through controlled enzyme reactions.

The page focuses on aerobic respiration, which requires oxygen:

Vocabulary: Aerobic respiration - The process of breaking down glucose in the presence of oxygen to release energy.

The equation for aerobic respiration is provided: Glucose + Oxygen → Carbon Dioxide + Water + Energy

Highlight: The energy released from the breakdown of glucose is used to generate ATP $Adenosine Triphosphate$, which is the energy currency of the cell.

The page mentions that Stage I of respiration takes place in the cytoplasm, implying that there are further stages that occur elsewhere in the cell $likely in the mitochondria, though this is not explicitly stated on this page$.

This information ties in with earlier topics on cell membrane structure and function, as well as the role of mitochondria in energy production, which are key concepts in National 5 Biology cell structure studies.

This page provides an overview of the structures found in different types of cells, including plant, animal, fungal, and bacterial cells. It highlights the key components and their functions within each cell type.

Vocabulary: Cytoplasm - The gel-like substance within a cell where chemical reactions occur.

Definition: Cell membrane - A selectively permeable barrier that controls the entry and exit of substances in and out of the cell.

The page illustrates the various organelles present in different cell types:

• Plant cells: Cell wall, nucleus, cytoplasm, mitochondria, ribosomes, chloroplasts, vacuole, and cell membrane
• Animal cells: Nucleus, cytoplasm, mitochondria, ribosomes, and cell membrane
• Fungal cells: Cell wall, nucleus, cytoplasm, mitochondria, ribosomes, and cell membrane
• Bacterial cells: Cell wall, cell membrane, cytoplasm, ribosomes, and genetic material $including plasmids$

Highlight: The presence of a cell wall in plant, fungal, and bacterial cells, but not in animal cells, is a key distinguishing feature.

Each organelle's function is briefly described, such as the nucleus being the site of DNA and controlling cell activities, mitochondria as the site of aerobic respiration, and chloroplasts as the location for photosynthesis in plant cells.