Plant And Animal Responses 5.1.5

Front 1

Tropisms

Back 1

A tropism is a growth movement of a part of a plant in response to a directional stimulus, this can be toward the stimulus (Positive tropism) or away from the stimulus (Negative tropism). Plant responses include a variety of tropisms: Phototropism, Geotropism, Hydrotropism, Thigmotropism, Chemotropism.

Front 2

Responses to Touch

Back 2

The leaflets of the touch-sensitive leaves fold in rapidly when touched, this causes rapid water uptake in cells. This is not considered a tropism as it is not related to the direction of touch.

Front 3

Responses to Herbivory

Back 3

Herbivory is the consumption of plants by herbivores. One response is to produce herbivore-repellent chemicals such as Tannins, Alakoids or Pheromones.

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Tannins (Responses to Herbivory)

Back 4

Stored in the vacuoles of plant cells, can be fatal to herbivorous insects. The bitter taste can also put off herbivores.

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Alakoids (Responses to Herbivory)

Back 5

They are bitter tasting and can be toxic, particuarly to herbivorous insects and sometimes fungi.

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Pheromones (Responses to Herbivory)

Back 6

May be directly toxic to herbivorous insects or trigger other chemical defences in some plants.

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Responses to Abiotic Stress

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Abiotic Stress can occur in various forms: Freezing, Drought, Water Salinity increases, Presence of Heavy Metals.

Front 8

Drought (Responses to Abiotic Stress)

Back 8

Plants can respond to drought by shutting their stomata - reducing water loss through transpiration - or by dropping their leaves.

Front 9

Freezing (Responses to Abiotic Stress)

Back 9

Some plants can respond to temperatures below freezing by producing an antifreeze chemical in their cells, that decreases the formation of ice crystals that can destroy plant cells.

Front 10

Phototropism in Plant Shoots

Back 10

Plant shoots are positively phototropic, meaning they grow towards light. This ensures they maximise the amount of light they can absorb for photosynthesis.

Front 11

IAA

Back 11

IAA is an auxin that is a specific growth factor in plants. IAA is synthesised in the growing tips of roots and shoots, as well as in the meristem and passed down the stem. The IAA has active proteins known as expansins which loosen the bonds in the cell wall making it more flexible and causing it to absorb more water and elongate.

Front 12

Phototropic Mechanism

Back 12

In shoots, higher concentrations of IAA results in a greater rate of cell elongation. IAA moves to the shaded side of the shoot causing a faster rate of cell elongation so the shoot bends toward the light.

Front 13

Geotropism in Plant Shoots and Roots

Back 13

Gravity affects both plant shoots and roots but in different ways. When shoots grow away from gravity it is known as Negative Geotropism, IAA accumulates on the lower side so the shoot grows upwards. When the roots grow towards gravity it is known as Positive Geotropism. In roots higher concentrations of IAA results in a lower rate of cell elongation so as they accumulate on the lower side of the root it inhibits cell elongation causing the root to bend downwards.

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The role of hormones in Leaf Loss

Back 14

Deciduous plants lose their leaves in very hot and dry environmental conditions as well as temperate climates due to frozen soils, in order to reduce water loss. An abscission layer develops at the base of the leaf stalk and the hormone Ethene stimulates the breakdown of this layers.

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The role of hormones in Stomatal Closure

Back 15

During times of water stress the hormone ABA is produced to stimulate the closing of their stomata. Guard cells have ABA receptors, when ABA binds it inhibits the proton pumps and stops active transport of H+ ions. ABA also causes calcium ions to move into the guard cell cytoplasm. They cause channel proteins to open to allow negative ions to leave, but they also close the channels that allow potassium ions to enter. This causes water loss of the guard cells and they become flaccid so stomata close.

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The role of hormones in Seed Germination

Back 16

Gibberellins are a type of plant hormone involved in controlling seed germination and stem elongation. When the conditions are right, a seed will start to absorb water - stimulating the embryo to produce gibberellins. They diffuse into the aleurone layer and stimulate the cells to synthesis amylase. The amylase hyrolyses starch molecules producing soluable maltose molecules which is converted to glucose for respiration for energy which is needed to grow.

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Apical Dominance

Back 17

The auxins that are produced at the growing tip at the apex of a plant stem cause the stem to grow upwards and also stop lateral (side) buds from growing.

Front 18

Commercial uses of Plant Hormones

Back 18

Hormones can be used to benefit commercial plant growing in a variety of ways, including: Selective weed killers, Rooting powder and controlling ripening.

Front 19

Selective Weed Killers (Commercial uses of Plant Hormones)

Back 19

Auxins are usually growth-promoting, however in high enough concentrations they can cause such rapid growth that plant tissues become distorted and damaged, allowing pathogens to enter the plant. This treatment is effective against weeds as they are much more effected by this than other plants.

Front 20

Rooting Powders (Commercial uses of Plant Hormones)

Back 20

Auxins can be used to stimulate cuttings to grow new roots. These auxins, present at the correct dosage, are sold in the form of rooting powders - commonly used by florist businesses.

Front 21

The control of Ripening (Commercial uses of Plant Hormones)

Back 21

Ethene can be used to stimulate fruit to ripen. This is often used for fruits that are delicate and soft when they ripe and can be easily damaged during transport as a result. Instead they can be harvested unripe and hard then ripened artificially using ethene upon arrival.

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The Nervous System

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The Nervous System consists of the CNS - the brain and spinal cord - and the PNS - all of the nerves in the body. It allows us to make sense and respond to our surroundings as well as regulate body functions.

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The Somatic Nervous System

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This is required for the voluntary control of body movements. It consists of three nerves: Sensory nerves - Sensory neurones that carry impulses from sense organs to the CNS, Motor Nerves - Motor neurones that carry impulses from the CNS to muscles and glands, Spinal Nerves -found in the spinal cord and consist of both Sensory and Motor neurones.

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The Autonomic Nervous System

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The Autonomic Nervous System can be divided into two parts. The Sympathetic Nervous System which controls 'flight-or-fight' responses, and the Parasympathetic Nervous System which controls the 'rest amd digest' system

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The 'fight-or-flight' response

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The release of adrenaline, a hormone produced by the adrenal glands, is stimulated by the Sympathetic Nervous System. It increases heart rate causing muscles to be supplied with more blood which contains oxygen and glucose for respiration and therefore ATP.

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The Human Brain

Back 26

The brain, alongside the spinal cord, is part of our central nervous system (CNS), Within the brain are different regions that carry out different functions; Cerebrum, Hypothalamus, Pituatry Gland, Cerebellum and Medulla Oblongata.

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The Cerebrum

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The Cerebrum carries out a variety of functions involved with conscious activity: Vision, Hearing, Speech and Thinking.

Front 28

The Hypothalamus

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The Hypothalamus is found just above the pituatry gland. It releases hormones itself or stimulates the Pituitary Gland to release hormones involved in homeostasis e.g Regulating Body Temperature, Osmoregulation , Endocrine functions etc.

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The Pituitary Gland

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Located below the Hypothalamus. It produces a range of hormones, some of these directly influence and regulate the body but some stimulate the release of further hromones from specific areas.

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The Cerebellum

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Lies below the Cerebrum. It controls motor coordination e.g balance. It functions only subconsciously

Front 31

The Medulla Oblongata

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Found at the very base of the brain, where it joins the spinal cord. It contrains three 'centres': The cardiac centre- controls heart rate, the vasomotor centre- controls blood pressure and the respiratory centre - controls breathing rate.

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Reflex Actions

Back 32

They are Involuntary Responses to certain stimuli, they are very fast and usually have a protective purpose or survival value. e.g Yawning, Blinking, Swallowing. Some of these can also be carried out on purpose. The Sequence is as follows : Stimulus, Receptor, Coordinator (Spinal Cord), Effector and Response.

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The Knee-jerk Reflex

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Used by doctors to assess whether the nervous system of a patient is working or not. Doctors use a specialised hammer to hit a ligament between the knee cap and the tibia.

Front 34

The Blinking Reflex

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Blinking is a reflex response caused by something travelling towards the eye at high speed, something contacting the cornea, or by drying of the cornea.

Front 35

Controlling the Heart Rate (Autonomic Nervous System)

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The Medulla is the Cardioregulatory Centre and controls the heart rate. It is made up of two distinct parts, the Acceleratory Centre and the Inhibitory Centre. Both centres are connected to the SAN.

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The Acceleratory Centre

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Once the Acceleratory Centre has been activated impulses are sent along the Sympatheitc Neurones to the SAN. Noradrenaline is secreted causing the SAN to increase the frequency of electrical waves, increasing the heart rate.

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The Inhibitory Centre

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Once the Inhibitory Centre has been activated, impulses are sent along the Parasympathetic neurones to the SAN. Acetylcholine is secreted is secreted causing the SAN to reduce the frequency of the electrical waves, reducing the heart rate.

Front 38

Factors affecting Heart Rate Table

Back 38

Front 39

Skeletal (Voluntary) Muscle

Back 39

Striated muscle that makes up the muscles that are attatched to the skeleton, allows movement of bones/skeleton.

Front 40

Smooth (Involuntary) Muscle

Back 40

Vital for unconscious control of many body parts, similar to skeletal muscle it contains both actin and myosin however it does not have any striations. Present in the walls of blood vessels and allows them to narrow, also allows contraction and peristalsis.

Front 41

Cardiac Muscle

Back 41

Only present within the heart, it is myogenic meaning it can contract without external stimulation. This allows the heart to beat at its own regular intervals. Cardiac muscle fibres are connected to each other via connections called intercalated discs.

Front 42

Muscle Fibre

Back 42

Each muscle fibre is surrounded by a cell surface membrane and contains many nuclei. The cell surface membrane is known as the sarcolemma which has many deep projections known as T-Tubules, the cytoplasm is the sarcoplasm and the endoplasmic reticulum is the sarcoplasmic reticulum (SR).

Front 43

Myofibrils

Back 43

Located in the sarcoplasm, each myofibril is made up of two types of protein filament : thick filaments made of myosin, thin filaments made of actin. These filaments are arranged to create bands and lines.

Front 44

Thick Filaments (Myosin)

Back 44

Fibrous protein molecules with a globular head, the fibrous part of the myosin molecule anchors the molecule into the thick filament. Many myosin molecules lie next to each other with their globular heads all pointing away from the M line.

Front 45

Thin Filaments (Actin)

Back 45

Globular protein molecules, many actin molecules link together to form a chain. Two actin chains twist together to form one thin filament.