GCSE Biology Paper 1 (Foundation) Study Guide

CELL BIOLOGY: STRUCTURES AND FUNCTIONS

Cell biology is the fundamental study of the basic units of life. The cell is composed of several key structures with specialized functions. The cell membrane is responsible for controlling the movement of substances entering and exiting the cell. The cytoplasm serves as the medium where most chemical reactions within the cell take place. The nucleus acts as the control center for cell activities and contains the genetic material necessary for reproduction and function. Mitochondria are the organelles where aerobic respiration occurs, providing energy for the cell. Ribosomes are the specific sites for protein synthesis. These basic structures are found in various types of cells, including general animal and plant cells. Specifically, specialized cells are adapted for their functions: nerve cells are long to carry electrical impulses; muscle cells are designed to contract to facilitate movement; and sperm cells possess a tail for swimming, many mitochondria to provide energy for movement, and a nucleus containing a haploid number of chromosomes.

CELL BIOLOGY: MICROSCOPY

To study these microscopic structures, scientists use microscopes. Two primary measurements in microscopy are resolution and magnification. Resolution is defined as the ability to see detail and is calculated using the formula: $\text{resolution} = \frac{\text{size of real object}}{\text{size of image}}$. Magnification indicates how many times bigger the image appears compared to the real object and is calculated as: $\text{magnification} = \frac{\text{size of image}}{\text{size of real object}}$. Key components of a microscope include the eyepiece lens and the objective lens, which work together to produce a detailed image of cells or microorganisms.

ORGANISATION in ANIMALS AND THE CIRCULATORY SYSTEM

Living organisms exhibit levels of organization starting from the basic unit of life. The hierarchy is: Cell (\rightarrow) Tissue (\rightarrow) Organ (\rightarrow) Organ System (\rightarrow) Organism. For example, muscle tissue (a tissue) makes up the heart (an organ), which is part of the circulatory system (an organ system). The human body utilizes a double circulatory system where the heart pumps blood throughout the body. There are three main types of blood vessels: arteries, which carry blood away from the heart at high pressure and have thick walls; veins, which carry blood toward the heart, have thin walls, and contain valves to prevent backflow; and capillaries, which are very small vessels that facilitate the exchange of substances between the blood and tissues.

THE RESPIRATORY AND DIGESTIVE SYSTEMS

In the respiratory system, air is breathed in and out of the lungs following a pathway from the nose or mouth through the trachea, into the bronchi, then the bronchioles, and finally reaching the alveoli. Alveoli are tiny air sacs that provide a large surface area and have a good blood supply, making them ideal for gas exchange. The digestive system processes food through a pathway consisting of the mouth, oesophagus, stomach, small intestine, large intestine, and anus. Digestion is facilitated by enzymes: amylase in the mouth breaks down starch into sugars; protease in the stomach breaks down proteins into smaller proteins; and lipase in the small intestine breaks down fats into fatty acids and glycerol.

INFECTION AND RESPONSE: PATHOGENS AND DEFENCES

Communicable diseases are caused by pathogens, which include bacteria, viruses, fungi, and protists. These pathogens can be spread through the air, water, direct contact, or biological vectors. Prevention strategies include good hygiene, vaccines, and the use of antibiotics, though antibiotics are only effective against bacteria. The human body has non-specific (innate) defence systems, such as the skin acting as a physical barrier, mucus and cilia which trap pathogens, stomach acid that kills ingested pathogens, and white blood cells that destroy them. Fever is another defence that slows the reproduction of pathogens. The specific (adaptive) immune system involves lymphocytes, which produce antibodies to destroy pathogens or their toxins, and memory cells, which provide a faster immune response upon subsequent exposures. Vaccination involves introducing a dead or weakened pathogen or its antigens to stimulate the production of memory cells.

BIOENERGETICS: PHOTOSYNTHESIS AND RESPIRATION

Bioenergetics involves the transfer of energy in living systems. Photosynthesis is the process by which plants use light energy to produce glucose. The word equation is carbon dioxide + water (\rightarrow) glucose + oxygen, and the chemical equation is: $6CO_2 + 6H_2O \rightarrow C_6H_{12}O_6 + 6O_2$. This occurs in chloroplasts where chlorophyll absorbs light energy. Respiration is the breakdown of glucose to release energy for life processes, occurring primarily in the mitochondria. The word equation for aerobic respiration is glucose + oxygen (\rightarrow) carbon dioxide + water. The chemical equation is: $C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + \text{energy}$. Aerobic respiration requires oxygen and releases a lot of energy. Anaerobic respiration does not require oxygen and releases only a little energy; in animals, it produces lactic acid: $C_6H_{12}O_6 \rightarrow \text{lactic acid} + \text{energy}$, while in yeast, it produces ethanol and carbon dioxide: $C_6H_{12}O_6 \rightarrow \text{ethanol} + CO_2 + \text{energy}$.

HOMEOSTASIS, RESPONSE, AND INHERITANCE

Homeostasis and response involve the regulation of the internal environment and reactions to stimuli. The nervous system facilitates very fast reflex actions involving cell bodies and electrical impulses. Hormones are chemical messengers carried in the blood that act on specific target organs; examples of blood sugar regulation involve insulin and glucagon. In the study of inheritance, genes are passed from parents to offspring. Each individual carries genetic information that determines variation and evolution.

FOOD TESTS AND KEY PRACTICALS

Testing for biological molecules is a key component of biology practicals. For starch, iodine solution changes from orange-brown to blue-black in a positive result. Reducing sugars are tested with Benedict\'s solution, which changes from blue to green, yellow, orange, or brick-red upon heating. Proteins are detected with Biuret solution, changing from blue to lilac. Lipids are identified using the ethanol emulsion test, where a clear solution turns cloudy white. Essential practicals for Paper 1 include using a microscope to observe cells and microorganisms, performing food tests, investigating enzyme activity, and observing osmosis in plant tissue or transpiration in plants.