Edexcel Biology GCSE - Key Concepts in Biology

Egg cells are designed to accept one sperm and develop into an embryo.

The egg cell membrane only accepts one sperm. It becomes impenetrable after fertilization.

Move bacteria to the stomach where they're digested.

Absorb water and minerals from soil. Specialized for water absorption.

They have a large surface area to absorb more water and minerals.

Transport water and minerals up the plant.

Hardens xylem cells, making them strong enough to transport water.

Xylem cells are hollow, joined end-to-end, and contain lignin.

Phloem cells are specialized to transport food (products of photosynthesis) throughout the plant.

Structures formed by the breakdown of cell walls in phloem cells, allowing substance movement between cells.

The energy needed for phloem cell function is supplied by mitochondria in companion cells.

A light microscope enlarges images, allowing viewing of tissues, cells, and large sub-cellular structures.

Electron microscopes provide higher magnification and resolution to view sub-cellular structures like ribosomes and viruses in great detail.

Electron microscopes come in scanning (3D images) and transmission (2D images) varieties.

Electron microscopes are used to study viruses and proteins in far greater detail than light microscopes.

Electron microscopes have a resolving power much higher than light microscopes, allowing for greater detail.

Enzymes are biological catalysts, meaning they speed up reactions without being used up. They are essential for many biological processes, including breaking down large molecules and joining small ones.

The active site is the unique, 3D shaped region on an enzyme where the substrate binds.

This hypothesis explains how enzymes work. The shape of the substrate is complementary to the active site, allowing them to bind and form an enzyme-substrate complex.

Enzymes have specificity, meaning they can only catalyze reactions for substrates that have a complementary shape to their active site.

Each enzyme has an optimum temperature where it functions best. Above or below this temperature, the enzyme's activity decreases, potentially leading to denaturation.

When an enzyme loses its shape due to extreme temperatures (above optimum) or pH changes, it can't bind to its substrate and becomes inactive.

Most enzymes have an optimum pH of around 7 (neutral). However, some enzymes, like those in the stomach, function best in acidic conditions.

Enzyme activity is also affected by the concentration of the substrate. As the substrate concentration increases, the rate of reaction also increases up to a point, after which the enzyme becomes saturated.

The process of building new carbohydrates, lipids, and proteins from simpler molecules.

Special enzymes are required to accelerate the reactions that build carbohydrates, lipids, and proteins.

Specific tests used to identify the presence of different nutrients like starch, sugars, protein, and lipids in food samples.

A test using iodine solution to detect starch in a food sample. A color change from orange to blue-black indicates the presence of starch.

A test using Benedict's solution to detect reducing sugars in a food sample. A color change to reddish-brown indicates the presence of reducing sugars.

A blue solution used in the reducing sugars test to detect the presence of sugars that can reduce copper ions.

A method used to heat the sample and Benedict's solution in the reducing sugars test, providing the necessary heat for the reaction.

A practical experiment to identify the presence of different macronutrients (carbohydrates, lipids, and proteins) in food samples using specific tests.

When an enzyme's shape is altered by factors like extreme pH, making it unable to bind to its substrate. This is irreversible and results in loss of enzyme activity.

The specific region on an enzyme where the substrate binds, allowing the chemical reaction to occur.

The rate of an enzymatic reaction increases as the substrate concentration increases, but only up to a certain point.

The point where adding more substrate will not increase the reaction rate because all active sites of the enzyme are occupied.

An enzyme that breaks down carbohydrates like starch into simpler sugars like maltose.

Iodine solution turns blue-black in the presence of starch.

The specific pH value that allows an enzyme to function at its maximum rate.

By testing amylase activity at different pH levels, we can determine the pH value at which it functions best.

A chemical test to detect the presence of proteins in a sample. It involves adding potassium hydroxide and copper sulfate solution, which turns the solution violet if protein is present.

A test to identify the presence of lipids (fats and oils) in a sample. Ethanol is added to the sample, followed by water, leading to a milky white emulsion layer forming on top if lipids are present.

A standard sample used as a reference in an experiment. Controls help determine whether the results are due to the variable being tested or other factors.

A technique used to measure the energy absorbed or released during a chemical reaction, such as burning food to determine its caloric content.

Calorimetry involves 1) heating a known volume of water, 2) recording its initial temperature, 3) burning a food sample to heat the water, and 4) recording the final temperature to calculate the calories in the food.

A control sample that is known to contain the variable being tested, ensuring the test is working correctly.

A control sample that does not contain the variable being tested, ensuring the test is not giving false positives due to other factors.