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Plants Respond to Stimuli

Tropism: a directional growth response in which the direction of the response is determined by
the direction of the external stimulus.

PhototroPism: shoots grow towards light ­ enables them to photosynthesise.
GeotroPism: roots grow towards the pull of gravity.
ChemotroPism: attracted towards…

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The cell wall is highly restrictive, so therefore growth only happens in particular places in
-Apical meristems: located at the tips (apices) ­ responsible for the roots and shoots
getting longer.
-Lateral bud meristems: are found in buds. These could give rise to side shoots.
-Lateral meristems: are found…

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-ABSCISIC acid (AA) inhibits bud growth. High concentrations of auxin in the shoot may keep AA
levels high in the bud. When auxin is removed, AA drops ­ bud grows.
-Cytokinins (CK) promote bud growth. High conc of auxins make the shoot apex a sink for CK ­
produced in…

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CYTOKININS: can delay yellowing of lettuce leaves after being picked.
Used in tissue culture to help mass-production ­ promote bud and shoot growth from small
pieces of tissue taken from parent plants.

ETHENE: cannot be sprayed directly gas.
2-chloroethylphosphonic acids ­ can be sprayed in a solution.
Speeds up fruit…

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Medulla Oblongata: controls action of smooth muscle in the gut wall, and controls breathing
movements and heart rate.

Organising the Nervous System

Subdividing the Nervous System

The nervous system coordinates actions of the body through electrical impulses. It works in
conjunction with the endocrine system.

The central and peripheral nervous…

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The Elbow ­ A closer look
An example of a synovial joint ­ a lot of movement is needed. Synovial fluid is a lubricant, eases
movement of the bone at the joint. The biceps and triceps act antagonistically in order to move
the forearm at the elbow.

Impulses arriving at…

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wall and and the
cervix of redirecting of
uterus blood to
muscles during

Contractions are relatively slow, tires slowly.

Cardiac Muscle:
Atrial muscle
Specialised excitatory and conductive muscle fibres. ­ Contract feebly, but conduct electrical
impulses and control the rhythmic heartbeat. The SINOATRIAL NODE is made up…

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Many mitochondria
Extensive sarcoplasmic reticulum
A number of myofibrils; contractile element ­ each consists of a chain of smaller
contractile units called sarcomeres. Within the myofibrils there are two types of
myofilaments: THIN actin and THICK myosin ­ these run the length of the cell.
This type of muscle contracts…

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calcium ions are released from the sarcoplasmic reticulum in the sarcomeres the Ca ions
travel through the sarcoplasm and bind to the troponin molecules ­ this changes the shape of
the troponin, which in turn moves the tropomyosin away from the binding sites on the actin.


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Innate Behaviour

Innate behaviour is any animal response that occurs without the need for learning.

Innate Behaviours Learned Behaviours
Genetically Determined by the
determined ­ not relationship between
impacted on by the the genetic make-up
environment. Passed of the individual and
onto offspring. environmental
influences. May be
passed on by…


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