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Biology - Coordination and Response

Grade 10IGCSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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The Nervous System consists of the Central Nervous System (CNS) - the brain and spinal cord - and the Peripheral Nervous System (PNS). Signals are transmitted as electrical impulses along neurons at speeds up to 100 m/s100\text{ m/s}.

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A Reflex Arc is an involuntary, rapid response to a stimulus. The pathway is: Stimulus→Receptor→Sensory Neuron→Relay Neuron (CNS)→Motor Neuron→Effector→Response\text{Stimulus} \rightarrow \text{Receptor} \rightarrow \text{Sensory Neuron} \rightarrow \text{Relay Neuron (CNS)} \rightarrow \text{Motor Neuron} \rightarrow \text{Effector} \rightarrow \text{Response}.

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Synapses are junctions between neurons. When an impulse reaches the end of an axon, neurotransmitters are released into the synaptic cleft, diffusing across to bind with receptor molecules on the postsynaptic membrane.

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The Human Eye performs accommodation to focus on objects. For distant objects, ciliary muscles relax and suspensory ligaments pull tight, making the lens thin. For near objects, ciliary muscles contract and suspensory ligaments slacken, making the lens thick and convex.

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Hormones are chemical substances produced by endocrine glands and carried by the blood to target organs. For example, Adrenaline prepares the body for 'fight or flight' by increasing heart rate and blood glucose concentration (C6H12O6C_6H_{12}O_6).

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Homeostasis is the maintenance of a constant internal environment. Insulin and Glucagon work antagonistically to maintain blood sugar levels near a set point of approximately 5 mmol/dm35\text{ mmol/dm}^3.

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Plant Tropisms are growth responses. Phototropism is a response to light, and Gravitropism (Geotropism) is a response to gravity, both controlled by the distribution of the hormone Auxin.

📐Formulae

Magnification=Image sizeActual size\text{Magnification} = \frac{\text{Image size}}{\text{Actual size}}

C6H12O6+6O2→6CO2+6H2O+Energy (ATP)C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + \text{Energy (ATP)}

Reaction Time=2×distanceg\text{Reaction Time} = \sqrt{\frac{2 \times \text{distance}}{g}}

💡Examples

Problem 1:

Explain how the eye focus changes when a person looks from a book (near) to a distant tree.

Solution:

  1. The ciliary muscles relax. 2. The suspensory ligaments become tight (strained). 3. The lens is pulled into a thinner, less convex shape. 4. Light rays are refracted less to focus on the retina.

Explanation:

To focus on distant objects, the eye needs less refractive power because the incoming light rays are nearly parallel. A thinner lens provides this lower refractive power.

Problem 2:

Describe the distribution of auxin in a plant shoot exposed to light from one side (unidirectional light).

Solution:

Auxin is produced in the shoot tip and moves away from the light source, accumulating on the shaded side of the shoot. This high concentration of auxin causes cells on the shaded side to elongate more than cells on the light side.

Explanation:

Because the cells on the shaded side grow longer than those on the lit side, the shoot bends towards the light source (extpositivephototropism ext{positive phototropism}).

Problem 3:

In the control of blood glucose, what happens when the concentration of C6H12O6C_6H_{12}O_6 in the blood rises above normal levels?

Solution:

The pancreas detects the increase and secretes the hormone Insulin. Insulin travels in the blood to the liver, stimulating it to convert excess glucose into insoluble glycogen for storage.

Explanation:

This is an example of negative feedback, where the response (lowering blood sugar) opposes the initial stimulus (high blood sugar).

Coordination and Response - Revision Notes & Key Formulas | IGCSE Grade 10 Science