Chapter 1: Stimuli and Responses - 1.3-1.4

Formative Practice 1.2 & Activity 1.9

  • Topics Include:

    • Optical illusions and blind spots.

    • Audio-visual defects (short-sightedness, long-sightedness, astigmatism, hearing defects).

    • Correction of audio-visual defects using concave/convex lenses and hearing aids.

    • Examples and effects of unhealthy lifestyles/high-risk careers on sensory organs.

    • The five senses as a gift, emphasizing safety and healthcare of sensory organs.

    • CPS, ISS, ICS (likely related to sensory or technological applications).

  • Mechanism of Sight (Fill in the Blanks):

    • Light → (a) → Aqueous Humor → (b) → (c) → Eye lens → Optic nerve → Vitreous Humor → (d)

  • Questions:

    • Which ear structure, if damaged, won't affect hearing?

    • Where are smell sensory cells located?

    • Five tastes detectable by the tongue.

    • Two factors influencing skin sensitivity to stimuli.

    • Stimulus type detected by the tongue and detection method.

Experiment 1.1 & Section 1.3: Stimuli and Responses in Plants

Responses of Plants to Stimuli (Figure 1.24)

  • Plants, like animals, detect and respond to stimuli: light, water, gravity, touch.

  • Responses divided into Tropism and Nastic movement.

Tropism

  • Definition: Directional response to stimuli from a specific direction.

  • Plant part grows toward (positive tropism) or away (negative tropism) from the stimulus.

  • Response is slow and subtle.

Nastic Movement

  • Definition: A non-directional response to a stimulus.

Experiment 1.1: Response of Plants to Light (Phototropism)

  • Aim: Study plant response to light.

  • Problem Statement: Which plant part responds to light?

  • Hypothesis: Shoots grow toward light.

  • Variables:

    • Manipulated: Light direction towards seedlings.

    • Responding: Shoot growth direction.

    • Constant: Seedling type/height, water volume.

  • Materials: Green pea seedlings, soil, water, three boxes (one open, two with side openings).

  • Procedure:

    • Set up seedlings in boxes A, B, and C (Figure 1.25).

    • Observe and sketch shoot positions in each box.

    • Keep boxes in the lab for five days, maintaining moist soil.

    • After five days, observe and sketch shoot positions again.

  • Conclusion: Determine if the hypothesis is accepted based on observations.

Questions

  • What is the stimulus used in this experiment?

  • State the part of the plant that responds to the stimulus.

  • Does the part of the plant in question 2 show positive or negative phototropism? Explain your answer.

B: Response of Plants to Gravity (Geotropism)

  • Aim: Study plant response to gravity.

  • Problem statement: Which part of plants responds to gravity?

  • Hypotheses:

    • Roots grow in the direction of gravity.

    • Shoots grow opposite to gravity.

  • Variables:

    • Manipulated: Seedling position relative to gravity.

    • Responding: Root and shoot growth direction.

    • Constant: Water presence, light absence, seedlings with straight roots/shoots.

  • Materials: Green pea seedlings with straight roots/shoots, moist cotton wool, plasticine.

  • Apparatus: Petri dish.

  • Procedure:

    • Set up in Petri dish with seedlings in different positions (Figure 1.26).

    • Observe and sketch shoot/root positions.

    • Keep in a dark cupboard for two days.

    • Observe and sketch shoot/root positions again.

  • Conclusion: Determine if hypotheses are accepted.

Questions

  • Why keep the apparatus in a dark cupboard?

  • Based on observations, state the growth direction of shoots and roots.

  • Do plants show positive or negative geotropism? Explain why.

C: Response of Plants to Water (Hydrotropism)

  • Aim: Study plant response to water.

  • Problem statement: Which part of plants responds to water?

  • Hypothesis: Roots grow towards water.

  • Variables:

    • Manipulated: Presence of water source.

    • Responding: Root growth direction.

    • Constant: Gravity, light absence, seedlings with straight roots.

  • Materials: Seedlings with straight roots, moist cotton wool, anhydrous calcium chloride.

  • Apparatus: Rough wire gauze, two beakers.

  • Procedure:

    • Set up apparatus as in Figure 1.27.

    • Observe/sketch root positions in beakers X and Y.

    • Keep in dark cupboard.

    • Observe/sketch root positions after two days.

  • Anhydrous calcium chloride: Used to absorb moisture, creating a water gradient.

Questions

  • What is the stimulus used in this experiment?

  • State the part of the plant that responds to the stimulus.

  • What is the function of the anhydrous calcium chloride in Beaker Y?

  • Does the part of the plant in question 2 show positive or negative hydrotropism? Explain your answer.

Phototropism

  • Definition: Plant response to light.

  • Shoots show positive phototropism (grow towards light).

  • Ensures shoots and leaves get enough sunlight for photosynthesis.

Hydrotropism

  • Definition: Plant response to water.

  • Roots show positive hydrotropism (grow towards water).

  • Allows roots to obtain water for photosynthesis and absorb minerals.

Geotropism (Figure 1.29)

  • Definition: Plant response to gravity.

  • Roots show positive geotropism (downward growth).

  • Anchors the plant.

  • Shoots show negative geotropism (upward growth).

  • Allows shoots to reach sunlight for photosynthesis.

Thigmotropism

  • Definition: Plant response to touch.

  • Tendrils/twining stems show positive thigmotropism (cling to objects).

  • Enables plants to grow upwards and gain support.

  • Roots show negative thigmotropism (avoid objects).

Nastic Movement

  • Definition: Response to a stimulus (e.g., touch) that is independent of the direction of the stimulus.

  • More rapid than tropism.

  • Example: Mimosa sp. folds leaves inward when touched (Photograph 1.21).

  • Serves as defense.

Activity 1.10 & Formative Practice 1.3

  • Investigating plant responses in different situations.

  • Earth's gravity and sunlight exposure influence shoot/root growth.

  • Scientists at the International Space Station (ISS) study plant growth in:

    • No gravity.

    • Varying sunlight exposure periods.

  • Tropism: A growth response of a plant toward or away from a stimulus.

    • Touch: Thigmotropism

    • Gravity: Geotropism

    • Light: Phototropism

  • Plant Parts and Tropism:

    • Positive phototropism: Shoots

    • Positive geotropism: Roots

    • Positive thigmotropism: Tendrils, twining stems

  • Importance of Hydrotropism: Allows roots to obtain water.

  • Tropism vs. Nastic Movement:

    • Similarity: Both are plant responses to stimuli.

    • Difference: Tropism is directional; nastic movement is non-directional.

  • Stereoscopic Vision (Figure 1.30a):

    • Eyes located in front of the head (e.g., humans, cats, owls).

    • Narrow field of vision.

    • Overlapping fields of vision.

    • Three-dimensional images.

    • Accurate estimation of distance, size, and depth.

    • Helps predators hunt.

  • Monocular Vision (Figure 1.30b):

    • Eyes located on opposite sides of the head (e.g., rats, chickens, rabbits).

    • Wide field of vision.

    • Non-overlapping or slightly overlapping fields of vision.

    • Two-dimensional images.

    • Prevents accurate estimation of distance, size, and depth.

    • Helps animals detect enemies.

  • Stereophonic Hearing (Figure 1.31):

    • Hearing using both ears.

    • Allows accurate determination of sound direction.

    • Ear closer to sound source receives sound earlier and louder.

    • Brain detects time/loudness difference to determine sound direction.

    • Helps predators locate prey and prey locate predators.

  • Different animals hear different sound frequencies.

  • Examples:

    • Elephant: 16 - 12,000 Hz

    • Dog: 67 - 45,000 Hz

    • Human: 20 - 20,000 Hz

    • Rat: 200 - 80,000 Hz

    • Sea Lion: 450 - 50,000 Hz

    • Bat: 2,000 - 110,000 Hz

    • Dolphin: 40 - 100,000 Hz

Activity 1.12 & Formative Practice 1.4

  • Sensory Organs and Survival:

    • Responses to stimuli ensure animal survival.

  • Examples:

    • Electric eel produces an electric field.

    • Lateral line in fish.

    • Secretion of pheromones.

  • Vision Types:

    • Stereoscopic and monocular.

  • Factor Determining Vision Type:

    • Eye location.

  • Vision of Primary Consumers:

    • Monocular vision allows a wider field of view to detect predators.

  • Importance of Stereophonic Hearing:

    • Determine the location of sound sources.

  • Example of Locating Sound in the Dark:

    • Determining location of a mewing cat by interpreting differences in sound arrival time and loudness between ears.

Summary

  • Stimuli and Responses

  • Humans

    • Human nervous system consists of:

      • Central nervous system (brain, spinal cord).

      • Peripheral nervous system (nerves).

    • Sensory organs (eye, ear, nose, skin, tongue).

    • Voluntary and involuntary actions.

    • Sensitivity to stimuli: light, sound, smell, touch, taste.

    • Mechanism of hearing and sight.

    • Stereoscopic vision (predators).

    • Monocular vision (prey).

    • Stereophonic hearing (uses both ears).

  • Plants

    • Sensitive to stimuli: Light, gravity, water, touch

    • Tropism:

      • Phototropism (light).

      • Geotropism (gravity).

      • Hydrotropism (water).

      • Thigmotropism (Touch)

    • Nastic movement.

    • Responses ensure sustainability and survival.

Summative Practice

  • Human Nervous System:

    • Peripheral nervous system: nerves connecting brain and spinal cord.

    • Brain is essential for voluntary actions.

    • Playing badminton is a voluntary action.

    • Impulses interpreted by the brain.

  • Eye Responses: Responses A and B as shown in Figure 2

    • These responses protect the eye, especially the retina, by preventing light of excessive intensity from entering the eye. During the solar eclipse, we should observe this event on the water surface in a basin of water.

  • Mechanisms of Hearing and Sight: Include flow charts for both.

  • Human Skin:

    • Fingertip used to detect Braille symbols due to higher receptor concentration.

    • Tongue is not classified as skin; possesses specialized taste receptors, differing from general skin receptors.

  • Importance of Sense of Smell:

    • Detecting hazards in the laboratory.

  • Plant Responses for Photosynthesis:

    • Phototropism (towards light) and hydrotropism (towards water).

  • Pak Dollah's Glasses Invention:

    • Using a transparent plastic bottle filled with water to create a magnifying effect for reading.