General Biology Overview

The growth response of a plant to a directional stimulus such as light, where the plant bends towards the light source.

A plant hormone that controls growth, particularly cell elongation.

Stimulation of cell elongation by IAA

Inhibition of cell elongation by IAA

A directional response of an organism to a stimulus, where the organism moves towards or away from the stimulus.

A non-directional response of an organism to a stimulus, where the organism changes its speed or rate of turning.

An involuntary response to a stimulus, involving a simple neural pathway with only three neurons.

A reflex arc that involves only three neurons - a sensory neuron, a relay neuron, and a motor neuron.

The membrane becomes more permeable to sodium ions (Na+), allowing them to move into the axon down their electrochemical gradient. This influx of positive charges causes the inside of the axon to become less negative, leading to depolarization.

A rapid, short-lasting change in the membrane potential of a neuron, caused by the rapid influx of sodium ions followed by the efflux of potassium ions.

The membrane becomes more permeable to potassium ions (K+), allowing them to move out of the axon down their electrochemical gradient. This efflux of positive charges restores the negative charge inside the axon, returning the membrane potential to its resting state.

A brief period after repolarization where the membrane potential becomes even more negative than the resting potential. This is caused by the delayed closure of potassium channels, leading to a slight overshoot of potassium ions leaving the axon.

The minimum level of depolarization that must be reached for an action potential to be triggered. If the threshold potential isn't reached, no action potential is generated.

A receptor that responds specifically to mechanical pressure, causing depolarization in its sensory neuron. This depolarization, called a generator potential, can trigger an action potential if it reaches threshold.

The process in which several receptors (such as rods in the retina) send signals to a single neuron, increasing the chance of reaching threshold and triggering an action potential. This enhances sensitivity.

The ability to distinguish between different stimuli or objects, which depends on the density of receptors and how they connect to neurons.

The ability to detect light, including color, which is determined by the types of photoreceptor cells and their pigments.

The ability to see in black and white, primarily used in dim light conditions. It is due to the presence of only one type of photoreceptor, called rods, in the retina.

The ability to see different colors, created by the presence of three different types of cone cells in the retina, each sensitive to a different color: red, green, and blue.

A difference in sensitivity to light between rods and cones in the retina: rods are more sensitive, while cones are less sensitive.

A difference in visual acuity between rods and cones: rods have lower acuity, while cones have higher acuity.

Acetylcholine, the neurotransmitter used at neuromuscular junctions, is broken down by the enzyme acetylcholinesterase. The products of this breakdown are then reabsorbed by the presynaptic neurone to prevent overstimulation of the muscle fibre.

Synapses are unidirectional because neurotransmitters are only produced and released from the presynaptic neurone. The receptors for these neurotransmitters are only found on the post-synaptic membrane, ensuring the signal travels in one direction only.

Synaptic summation refers to the combined effect of multiple impulses converging on a single post-synaptic neurone. This can lead to a rapid build-up of neurotransmitter, making it more likely that the post-synaptic neurone reaches its threshold and generates an action potential.

Spatial summation occurs when multiple pre-synaptic neurones release neurotransmitters onto the same post-synaptic neurone. This combined release of neurotransmitters can reach the threshold needed for an action potential to be generated.

Temporal summation involves a single pre-synaptic neurone releasing neurotransmitter multiple times in rapid succession. The cumulative effect of this repeated release can reach the threshold and trigger an action potential.

Inhibitory synapses use neurotransmitters that cause the post-synaptic membrane to become hyperpolarised. This occurs because chloride ions flow into the cell and potassium ions flow out, making the inside more negative relative to the outside. This makes it more difficult for the post-synaptic neurone to reach threshold and generate an action potential.

The combination of excitatory and inhibitory neurones forming synapses with the same post-synaptic neurone allows for precise control over whether an action potential is triggered. This ensures that the nervous system can respond effectively to a wide range of stimuli.

A neuromuscular junction is very similar to a synapse, but the receptors are located on the muscle fibre sarcolemma instead of the post-synaptic membrane. Additionally, the muscle fibre forms clefts to store enzymes like acetylcholinesterase.

A series of solutions of known concentrations, typically made by diluting a stock solution.

A graph that plots the absorbance of light against glucose concentration for a set of solutions with known concentrations.

A colorimetric technique used to detect the presence of reducing sugars (like glucose) in a solution, producing a colored precipitate.

An instrument used to measure the absorbance of light through a solution, allowing the determination of the concentration of a substance.

A type of variable that should be kept constant throughout an experiment to ensure fair testing and reliable results.

A factor in an experiment being tested, which is changed intentionally to observe its effect on a dependent variable.

The variable that is measured or observed in an experiment, whose value is dependent on the independent variable.

A measurement of the amount of light absorbed by a substance, used to determine the concentration of a solution.

Phosphocreatine is a molecule found in muscle cells that acts as a short-term energy store. It rapidly donates a phosphate group to ADP, regenerating ATP for muscle contraction. This process is anaerobic and does not produce lactic acid.

Slow twitch muscle fibers are specialized for endurance activities. They rely primarily on aerobic respiration for energy production, leading to slower fatigue. They have a high concentration of mitochondria, myoglobin, and capillaries to support this process.

Fast twitch muscle fibers are specialized for short, intense bursts of activity. They primarily rely on anaerobic respiration, leading to quick fatigue. They have a high concentration of glycogen and a lower density of mitochondria and myoglobin compared to slow twitch fibers.

Slow twitch muscle fibers are found in muscles used for posture and endurance activities. They are found in abundance in muscles such as the back, calves, and the legs of endurance runners.

Fast twitch muscle fibers are found in muscles used for quick movements. They dominate muscles like the biceps, eyelids, and the legs of sprinters.

Slow twitch fibers have a high concentration of myoglobin, a protein that binds and stores oxygen. This allows them to sustain aerobic respiration for longer periods.

Fast twitch fibers have lower levels of myoglobin and a high concentration of glycogen. They rely heavily on glycogen stores to fuel anaerobic respiration for rapid energy bursts.

Myoglobin is a protein found in muscle tissue that binds and stores oxygen. It gives muscle tissue its red color, and its concentration is higher in slow twitch fibers compared to fast twitch fibers.