GCSE Biology Paper 1 Review

Key Terminology and Fundamental Biological Concepts

Active transport is defined as the movement of particles against a concentration gradient, a process that requires the use of energy derived from respiration. In contrast, diffusion refers to the movement of particles from an area of high concentration to an area of low concentration across the cell membrane. Osmosis is a specific type of diffusion involving the movement of water from a dilute solution to a less dilute solution, which can also be described as moving from a high water concentration to a low water concentration.

Several organelles and cellular structures are essential for the survival and Function of living cells. The nucleus serves as the control centre of the cell and contains the genes. The cytoplasm is the site where the chemical reactions that keep the cell alive take place. The cell membrane is responsible for controlling what substances pass in and out of the cell. Mitochondria are the organelles where energy is released during the process of respiration, while ribosomes are the specific sites where proteins are manufactured. In plant cells, chloroplasts are where photosynthesis occurs, and the vacuole stores cell sap. Plant cells also possess a cell wall for structural support.

Stem cells are unspecialised cells that have the potential to develop into any other type of cell. In plants, the source of these stem cells is the meristem, which is found in the growing parts of the plant. For microscopy calculations, the total microscope magnification is determined by multiplying the eyepiece lens by the objective lens.

Cell Biology: Eukaryotic and Prokaryotic Structures

Cells are categorized into two primary types: eukaryotic and prokaryotic cells. Eukaryotic cells contain a nucleus which houses their chromosomes; examples include animal, plant, fungus, or protist cells. Prokaryotic cells do not have a nucleus and are typically much smaller in size. They may also contain plasmids, which are small rings of DNA. The development of microscopes over the last 200 years has significantly advanced the ability to study these cells and their internal structures in greater detail.

Magnification units often require conversion for calculations. To convert from millimeters to micrometers, the value is multiplied by 1000 ( $mm \rightarrow \mu m \times 1000$ ). Conversely, to convert from micrometers to millimeters, the value is divided by 1000 ( $\mu m \rightarrow mm \div 1000$ ). Comparison between tools shows that light microscopes provide low resolution and low magnification but are relatively cheap. Electron microscopes offer high resolution and high magnification but are expensive.

Cell Specialisation and Differentiation

As organisms develop, cells differentiate to form specialised types suited for specific functions. In animals, a sperm cell is specialised with a high number of mitochondria and ribosomes in the head to produce enzymes. Nerve cells are characterized by their long length and numerous branches called dendrites. Muscle cells contain a high number of mitochondria and ribosomes and serve as storage for glycogen. In plants, xylem cells have walls thickened with lignin to strengthen them into tubes, and phloem cells feature sections called sieves to assist in transporting substances such as dissolved sugars.

Required Practical 1: Microscopy and Observing Plant Cells

The procedure for preparing a slide involves several precise steps. First, a thin layer of onion membrane is placed on a glass slide using forceps. A drop of iodine is then used to stain the cells for better visibility. Finally, a glass cover slip is gently placed over the sample and tapped carefully to remove any air bubbles.

To view the slide, it is placed on the stage and the light is turned on. The user selects the lowest magnification objective lens first. While looking through the eyepiece, the coarse focus is turned until the image becomes visible. The fine focus is then adjusted until a clear image is formed. If higher magnification is needed, the objective lens is changed, and the fine focus is used to re-focus the image.

Cell Biology Review Questions I

Name the three cell parts (organelles) found in a plant cell but not in an animal cell.
How can you identify an eukaryotic cell from its structure?
What is the role of a ribosome?
Which organelle releases energy through respiration?
What is the role of the cell wall?
What structures are only found in prokaryotic cells?
Which are larger; prokaryotic or eukaryotic cells?
What feature do some bacterial (and some animal) cells have that enable it to move?
Which part of a light microscope is the glass slide placed on?
Which objective lens is selected first to produce a magnified image of a sample?
What is used to stain plant cells?
What is place on top of the slide, sample and stain?
What part of the microscope is used to focus the image and make it clear?
What are the advantages of using an electron microscope for viewing cells?
Convert $2.3\,mm$ into $\mu m$ .
How would we calculate the actual size of a cell using the image size and magnification?
Convert $570\,\mu m$ into $mm$ .
How is a root hair cell specialised?
Why would a cell contain more mitochondria than usual?
Describe the structure of phloem cells.
How are nerve cells specialised?
Why does a sperm cell require a lot of mitochondria?
How are xylem cells specialised?
What does cell differentiation mean?
How is plant cell differentiation different to animal cell differentiation?

Cell Division and Stem Cells

Before a cell can undergo mitosis, it must grow and increase its number of sub-cellular structures, including ribosomes and mitochondria. During this preparation phase, the DNA replicates to form two identical copies of each chromosome. In the process of mitosis, one set of chromosomes is pulled to each end of the cell, followed by the division of the nucleus. Finally, the cytoplasm and cell membranes divide, resulting in two identical cells.

Stem cells are undifferentiated cells capable of giving rise to many more cells of the same type and can differentiate into other types of cells. Embryonic stem cells can be cloned and made to differentiate into most different types of human cells. Adult stem cells, specifically those found in bone marrow, can form many types of cells, including blood cells. Plant stem cells are found in meristems and can differentiate into any type of plant cell throughout the entire life of the plant.

Required Practical 2: Osmosis in Plant Tissue

This practical investigation observes how the concentration of a surrounding solution affects the mass of plant tissue. The steps are as follows:

Use a cork borer to create 5 cylinders of plant tissue, usually potato, and cut them all to the same length.
Measure the initial mass of each piece using a top pan balance and the length with a ruler; record these in a table.
Measure out $100\,cm^3$ of each concentration of salt or sugar solution into labelled boiling tubes.
Place each piece of potato into a boiling tube and leave for 24 hours.
Remove the pieces and blot them with a paper towel.
Measure the final mass and length using a top pan balance and ruler, recording the results.
Calculate the percentage change in mass for each sample.

Transport Across Membranes

Effective transport in organisms depends on specific structural adaptations. Alveoli in the lungs and villi in the small intestine are structured to allow diffusion at a high or fast rate by having a large surface area and a thin membrane that provides a short diffusion path. In animals, an efficient blood supply further aids this process. The rate of diffusion can be influenced by the difference in concentrations (the concentration gradient), the temperature, and the surface area of the membrane.

Osmosis occurs through a partially permeable membrane, which allows small molecules to pass through while blocking large molecules. Active transport differs from diffusion as it moves substances from a low concentration to a high concentration ( $L \rightarrow H$ ) against the gradient. This requires energy from respiration, which explains why cells involved in significant active transport, such as root hair cells and epithelial cells on villi, contain a high density of mitochondria.

Cell Biology Review Questions II

What has to be replicated (copied) before the cell can divide?
What happens in the third stage of mitosis?
What word is used to describe the similarity of the two cells formed?
What type of organism contains meristems?
What is a stem cell?
Which type of animal stem cell can only become a small number of different cells rather than any type of cell?
What piece of equipment is used to ensure the surface area of each piece of potato is the same?
What piece of equipment is used to measure the mass before and after the experiment?
What happens to pieces of potato in dilute (high water concentration) solutions?
What should be done with the pieces of potato after they have been removed from the solution but before their mass is measured?
What factors affect the rate of diffusion?
Give an example in animals where diffusion would take place.
How are structures in organisms adapted for efficient diffusion?
Do substances move from a low concentration to a high concentration in diffusion?
What substance is being transported by osmosis?
What does partially permeable mean?
How is active transport different to diffusion?
Give an example of where active transport happens often in organisms.
Why do cells that carry out active transport often have a lot of mitochondria?

Biological Organisation and the Digestive System

Biological structures are organized into levels: cells are the basic building blocks, tissues are groups of cells with similar structure and function, organs are aggregations of tissues performing specific functions, and organ systems are groups of organs organized to form organisms.

The human digestive system consists of several organs with specialized functions. The mouth uses teeth and the tongue to chew food, while salivary glands release saliva containing enzymes. The oesophagus is a muscular tube that squeezes food down to the stomach. The stomach contains enzymes and hydrochloric acid, which kills bacteria, and its muscular walls churn the food. The small intestine is where digestion is completed and soluble food particles like glucose, amino acids, fatty acids, and glycerol are absorbed. The large intestine absorbs water. The liver produces bile, an alkaline solution stored in the gall bladder that neutralizes stomach acid and emulsifies fats.

Enzymes and Food Tests

Enzymes are biological catalysts that speed up the breakdown of insoluble food molecules. They have a specific shape called an active site that matches a substrate. Their activity is affected by factors such as temperature and pH. Amylase, produced in the salivary glands, pancreas, and small intestine, breaks starch into glucose. Protease, produced in the stomach, pancreas, and small intestine, breaks protein into amino acids. Lipase, produced in the pancreas and small intestine, breaks fats into fatty acids and glycerol.

Required Practical 3 involves several food tests:

Protein: Add Biuret’s reagent; a positive test turns the blue solution purple.
Starch: Add iodine; a positive test turns the orange solution black.
Fats: Add ethanol and water; a positive test turns the solution cloudy.
Glucose: Add Benedict’s reagent and heat in a water bath; a positive test turns the blue solution brick red.

Human Circulatory and Respiratory Systems

The human heart is a double pump; the left side pumps blood to the whole body, while the right side pumps blood to the lungs. It consists of the left and right atria and ventricles. Major vessels include the Vena Cava (from the body), Pulmonary Artery (to the lungs), Aorta (to the body), and Pulmonary Vein (from the lungs). Pacemaker cells in the right atrium control the heart rate. The left ventricle has a thicker wall than the right to facilitate pumping to the whole body.

There are three types of blood vessels. Arteries carry blood away from the heart, possessing thick muscular and elastic walls to withstand high pressure and a small lumen to maintain it. Capillaries have walls only one cell thick for a short diffusion pathway and a lumen just larger than a red blood cell. Veins carry blood back to the heart, featuring thin walls for low-pressure blood, a large lumen for low resistance, and valves to prevent backflow.

Blood consists of four components: red blood cells (RBCs), which contain haemoglobin to carry oxygen and have a bi-concave disc shape for a large surface-area-to-volume ratio ( $SA:V$ ); white blood cells, which fight pathogens; platelets, which are cell fragments that clot blood; and plasma, the liquid part that transports cells and dissolved substances like salts, urea, $CO_2$ , and hormones. RBCs are approximately $8\,\mu m$ in size.

Health Issues and Heart Disease

Coronary Heart Disease (CHD) occurs when coronary arteries, which supply heart muscle with glucose and oxygen, become narrowed or blocked by fatty deposits if cholesterol is high. This reduces blood flow and muscle contraction. Treatments include statins, which are daily medications to lower blood cholesterol (though they do not work immediately), and stents, which are mesh tubes inserted via surgery to hold arteries open and work immediately. Faulty heart valves, which may not open or close fully, can be replaced with man-made valves or donor transplants.

Cancer is defined as uncontrolled cell growth. Benign tumours are abnormal cells contained within a membrane in one area, whereas malignant tumours are cancer cells that are not in a capsule, invade neighbouring tissues, and can spread into the blood to form secondary tumours. Health is also affected by the interaction of diseases: immune system defects increase susceptibility to infectious diseases, viruses like HPV can trigger cervical cancer, pathogens can trigger allergies (e.g., asthma), and severe physical ill health can lead to mental illnesses like depression. Lifestyle factors such as obesity, drinking, and smoking are significant risk factors.

Required Practical: Effect of pH on Amylase

To investigate the effect of pH on the rate of reaction of amylase, follow these steps:

Add $2\,cm^2$ amylase solution, $2\,cm^2$ of starch solution, and $2\,cm^2$ of pH 2 buffer to separate test tubes in a water bath set at $37^\circ$ . Wait 10 minutes.
Add 2 drops of iodine solution to each well on a spotting tile.
Pour the amylase and pH 2 buffer into the starch solution.
Immediately take a sample with a pipette and add it to the first well of the spotting tile.
Repeat every 30 seconds until there is no colour change with the iodine.
Repeat the entire process using pH 4, pH 6, pH 8, and pH 10 buffers.

Plant Structure and Transport

Leaves are structured for efficient gas exchange and photosynthesis. The top layer is the waxy cuticle, followed by the upper epidermis, the palisade mesophyll (containing many chloroplasts), and the spongy mesophyll (with air spaces). Stomata are tiny pores on the underside of the leaf that allow oxygen and $CO_2$ to diffuse; they are surrounded by guard cells that can open and close the pore.

Transpiration is the movement of water from roots to leaves through xylem (hollow tubes strengthened by lignin). This one-way system is driven by evaporation through the stomata. The rate of transpiration increases with higher temperature, lower humidity, higher light intensity, and higher air movement. It can be measured using a scale to record the distance an air bubble moves over time to calculate volume uptake per minute. Translocation is the movement of dissolved sugars from leaves to the rest of the plant through phloem (tubes of elongated cells), acting as a two-way system.

Organisation Review Questions

What is an organ system?
What are groups of cells with a similar structure and function?
Give an example of an organ.
Put these into order, starting with the smallest: tissue, cell, organ system, organ.
What is an enzyme?
What is the name of the part of the enzyme that the substrate fits into?
Give two factors that affect how enzymes work.
Where are the salivary glands found?
What is the job of the oesophagus?
What is the job of the pancreas (in digestion)?
What is the job of the small intestine?
What is the function of the hydrochloric acid in the stomach?
Where is lipase released from?
Which enzyme is released in the stomach?
Which enzyme is found in the mouth?
Where is bile made?
Where is bile stored?
What are the two jobs of bile?
Which two chemicals are added to test for fats?
What is the colour change when Biuret is added to a food containing protein?
Which test needs to be placed in a water bath?
Which enzyme breaks down starch?
What are the products of fat digestion?
What are proteins made of?
What is the name of the tube that connects the throat to the lungs?
What is the name of the tubes that enter each lung?
What are the two jobs of the lungs?
Name the two types of cells in blood.
What are platelets and what do they do?
Name 3 substances plasma might have dissolved in it.
What chemical is found inside red blood cells?
What is the 3D shape of RBCs called and what is its advantage?
Which blood vessel returns blood to the heart from the lungs?
Which blood vessel carries blood away from the heart towards the body?
Which ventricle wall is thicker?
Where are pacemaker cells found?
Why is the heart known as a double pump?
Which blood vessels contain valves?
Which vessels carry blood under very high pressure?
In which blood vessels does diffusion take place?
Which blood vessels have thick muscular walls?
Which vessels have a wide lumen?
What do coronary arteries do?
What can block coronary arteries?
What will happen to the heart if they become blocked?
What temperature should the water bath be set at for the practical involving the effect of pH on amylase?
What is the name of the chemical used to test for the presence of starch?
What is the independent variable in the investigation of pH on amylase?
How do stents treat CHD?
How do statins treat CHD?
Give an advantage of using stents rather than statins to treat CHD.
What are the cells called that surround the stomata?
What is the job of the stomata?
What is the top layer of a leaf called?
Which tissue in a leaf has air spaces?
Which layer in the leaf contains cells with lots of chloroplasts?
What is transpiration?
What is translocation?
Which tissue carries out translocation?
Name 2 conditions that affect the rate of transpiration.
Describe how to investigate the rate of transpiration.
What is a benign tumour?
Why do benign tumours not spread?
How can malignant tumours spread?
Name a disease linked with obesity.
What is the job of a valve?
How can faulty valves be treated?
Give an example of when cancer can be triggered by a virus.
Give an example of an immune reaction that can be triggered by a pathogen.