All of AQA BIOLOGY Paper 1 - GCSE Revision

Cells

Definition of Cells

All life is composed of cells, which serve as the fundamental building blocks of life. Organisms can be classified into unicellular and multicellular categories based on the number of cells they contain.

Microscopy

• Visible with Light Microscope: A light microscope allows for the observation of the basic structure of cells, including the cell membrane and nucleus. However, it does not provide sufficient resolution to visualize subcellular structures such as organelles.

• Electron Microscope: An electron microscope reveals finer details within cells and their organelles due to its superior resolving power. This technology is crucial for understanding cellular components at a molecular level.

Size Calculation

• Magnification Formula: Magnification is calculated using the formula: Magnification = Image Size / Object Size. This allows scientists to determine how much larger an image appears compared to its actual size.

• Actual Cell Size: The actual size of a cell can be calculated by rearranging the magnification formula: Actual cell size = Image size / Magnification.

Types of Cells

• Eukaryotic Cells: Eukaryotic cells possess a defined nucleus that houses their DNA. Examples include plant and animal cells. These cells also contain various organelles that perform specific functions.

• Prokaryotic Cells: Prokaryotic cells lack a true nucleus; their DNA is located in a region called the nucleoid and is often in the form of a plasmid. Bacteria are primary examples of prokaryotic cells.

Cell Structure

• Cell Membrane: The cell membrane is semi-permeable, meaning it allows certain substances to pass while blocking others. It is critical for maintaining homeostasis within the cell by controlling entry and exit of substances.

• Cell Wall: Found in plant cells and bacteria, the cell wall provides structural support and protection. In plants, it is primarily made of cellulose, while bacterial cell walls may have peptidoglycan components.

• Cytoplasm: Cytoplasm is the liquid medium within the cell that houses organelles and is the site for many biochemical reactions.

• Mitochondria: Often referred to as the powerhouse of the cell, mitochondria are responsible for aerobic respiration, converting glucose and oxygen into ATP, which is used as energy.

• Ribosomes: These organelles are essential for protein synthesis. Ribosomes can be found either floating free in the cytoplasm or bound to the endoplasmic reticulum.

• Chloroplasts: Exclusive to plant cells, chloroplasts contain chlorophyll and are responsible for photosynthesis, transforming light energy into chemical energy.

• Vacuole: Plant cells typically contain a large central vacuole that stores nutrients, waste products, and helps maintain turgor pressure against the cell wall.

Bacterial Multiplication (Triple only)

• Bacteria reproduce asexually through a process called binary fission, where one cell divides into two identical daughter cells.

Practical Culturing of Bacteria

• Bacteria can be cultured in a Petri dish using aseptic techniques to prevent external contamination. This involves using sterile instruments and working near a flame to create an updraft.

• Incubation at 25°C is typically employed to observe bacterial growth, optimizing conditions for cellular replication.

• Calculating Growth Area: The area of bacterial colonies can be calculated using the formula A = πd²/4, where d is the diameter of the colony.

Mitosis Process

Mitosis is a form of cell division that results in two genetically identical daughter cells and is crucial for growth, repair, and asexual reproduction. The process includes several phases: prophase, metaphase, anaphase, and telophase, followed by cytokinesis which divides the cytoplasm.

Specialized Cells

• Specialized cells include nerve cells for signal transmission, muscle cells for contraction, and root hair cells for absorption of water and nutrients. Xylem cells transport water, while phloem cells transport sugars throughout the plant.

• Stem Cells: These are undifferentiated cells that possess the potential to develop into various cell types depending on environmental factors and signaling mechanisms.

• Cloning in Plants: Cloning techniques are used to prevent the extinction of species and to produce plants with desirable traits for agriculture.

Transport Mechanisms

• Diffusion: The movement of particles from regions of high concentration to low concentration is a passive process essential for gas exchange and nutrient uptake in cells.

• Osmosis: This refers specifically to the movement of water through a semi-permeable membrane, driven by concentration gradients of solutes. Practical experiments, such as measuring potato cylinders in sugar solutions, help illustrate osmosis by calculating changes in mass.

• Active Transport: Contrary to diffusion, active transport requires energy to move substances against their concentration gradient. An example includes the uptake of essential mineral ions by plant roots.

Organization of Cells

• Tissues: Tissues are composed of groups of similar cells working together to perform a specific function, such as cardiac tissue in the heart.

• Organs: Organs are formed by different types of tissues working in concert, like the heart which includes muscle, nervous, and connective tissues.

• Organ Systems: Organ systems comprise groups of organs that collaborate to carry out complex functions, such as the circulatory system which includes the heart, blood vessels, and blood.

Digestive System

The digestive system's primary role is to break down food into absorbable nutrients through a series of mechanical and chemical processes, primarily in the stomach and small intestine.

• Enzymes: Enzymes are biological catalysts that accelerate biochemical reactions critical to digestion. Examples include:

  • Amylase: Converts starches into simple sugars like glucose.

  • Proteases: Breaks down proteins into amino acids.

  • Lipases: Decomposes lipids into glycerol and fatty acids.

• Denaturation of Enzymes: Extreme pH levels or temperatures can denature enzymes, rendering them inactive.

• Food Tests: Various chemical tests can identify the presence of nutrients, such as iodine for starch, Benedict's solution for reducing sugars, and Biuret test for proteins.

Respiratory System

Understanding the respiratory system is vital for comprehending how organisms exchange gases necessary for cellular respiration.

• Breathing vs. Respiration: Breathing involves the mechanical process of inhaling oxygen and exhaling carbon dioxide, while cellular respiration refers to the biochemical processes that generate energy within cells.

• Air Pathway: The pathway of air in the respiratory system follows: Trachea ➔ Bronchi ➔ Bronchioles ➔ Alveoli. Gas exchange occurs in the alveoli where oxygen diffuses into the blood, and carbon dioxide is expelled.

• Heart Structure: The circulatory system operates on a double circulatory structure, whereby deoxygenated blood is sent to the lungs for oxygenation, and oxygenated blood is distributed to the rest of the body. Heart valves prevent backflow, and coronary arteries supply blood to the heart muscle itself.

Cardiovascular and Non-communicable Diseases

Understanding the risk factors associated with cardiovascular diseases (CVD) is paramount as they are often influenced by lifestyle choices such as diet, exercise, and smoking.

• Types of Diseases: Diseases can be categorized into non-communicable (such as Type 2 diabetes and certain cancers) that are not transmitted between people, and communicable diseases that are caused by pathogens.

Plants and Transport

• Plant Organs: The leaf is responsible for photosynthesis, the root absorbs water and minerals, and the stem serves as structural support besides transporting nutrients.

• Transpiration: This process involves the loss of water vapor from plant leaves, which enhances nutrient uptake and occurs more rapidly with increased temperature and airflow.

• Xylem and Phloem: Xylem facilitates one-way water transport from roots to leaves, while phloem transports sugars and nutrients in both directions throughout the plant.

Infection and Immune Response

Pathogens such as viruses, bacteria, fungi, and protists can cause diseases; understanding their mechanisms of action is essential for managing health.

• Immune Response: The immune system employs white blood cells, including lymphocytes which produce antibodies that neutralize pathogens and phagocytes that engulf and destroy invaders.

• Vaccines: These are preparations that expose the immune system to pathogen antigens, priming it for future encounters.

• Antibiotics: Effective in treating bacterial infections, antibiotics do not work against viruses, and their misuse can lead to antibiotic resistance.

• Monoclonal Antibodies (Triple): Engineered antibodies used for diagnosing and treating various diseases are generated from a single clone of immune cells, making them highly specific.

Photosynthesis and Respiration

• Photosynthesis Equation: Photosynthesis can be summarized by the equation: Light energy + CO2 + H2O ➔ Glucose + O2. This endothermic process is essential for converting light energy into chemical energy stored in glucose.

• Factors affecting Rate: The rate of photosynthesis is influenced by light intensity, carbon dioxide concentration, and temperature, which can act as limiting factors in natural settings.

• Respiration Types:

  • Aerobic Respiration: Takes place in the presence of oxygen and yields the most ATP.

  • Anaerobic Respiration: Occurs without oxygen, resulting in byproducts like lactic acid in animals or ethanol and carbon dioxide in yeast, which are less efficient than aerobic respiration.

Metabolism

• Definition: Metabolism encompasses all chemical reactions within an organism, including catabolism (breaking down molecules to obtain energy) and anabolism (synthesizing complex molecules from simpler ones). This interplay is crucial for maintaining life.