IGCSE Biology

B9: Coordination & Response

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nerve impulse

an electrical signal that passes through neurons

CNS

central nervous system: brain & spinal cord

PNS

peripheral nervous system: receptor, motor neuron, sensory neuron

reflex arc

* a stimuli affects the receptor
* the sensory neuron carries impulse from receptor to CNS
* relay neuron carries impulse across spinal cord
* motor neuron carries impulse from CNS to effector
* effector carries out response

voluntary action

* involves brain


* conscious thought, decision making
* 1 stimuli may have different responses
* response is slower

involuntary action

* does not involve brain
* no conscious thought, automatic
* response always the same
* quick, rapid response

structure of the eye

* ciliary muscle: controls thickness of lens
* lens: focus light on retina
* iris: controls how much light enter pupil
* suspensory ligaments: hold lens
* cornea: refracts light
* nerve: send impulse to brain
* retina: contains light receptors

pupil reflex: dim light

* pupil dilates
* radial muscle contract
* circular muscle relax

pupil reflex: bright light

* pupil contracts
* radial muscle relax
* circular muscle contract

accommodation: near object

* suspensory ligaments slacken
* ciliary muscle contracts
* lens thicker

accommodation: far object

* suspensory ligaments stretches
* ciliary muscle relax
* lens thinner

hormone

a chemical substance produced by a gland, travel through bloodstream to change the activity of an organ

adrenaline

* adrenal gland
* prepare body in ‘fight or flight’ mode
* increase breathing/pulse rate,/glucose level, pupil dilates

insulin

* produced in pancreas, act in liver
* decrease blood glucose level

testoterone

* male sex hormone
* testes

oestrogen

* female sex hormone
* ovaries

effects of adrenaline

* increase breathing rate: supply oxygen for respiration → release energy
* increase pulse rate: blood carries oxygen to cells more quickly for respiration
* increase blood glucose level: more glucose for respiration
* pupil dilates: more light reaches retina, more information sent to brain

nervous system

* short term
* electrical impulses travel through neurons
* not localised
* fast

endocrine system

* long term
* chemical substances travel through bloodstream
* localised
* slower

homeostasis

the maintenance of a constant internal environment

negative feedback

* when the concentration of a substance is too high/low, corrective mechanisms will be activated
* when the concentration returns to normal, corrective mechanisms will be turned off

blood glucose level

* insulin: converts glucose into glycogen → lowers blood glucose level
* glucagon: converts glycogen into glucose → increase blood glucose level
* these hormones are secreted in pancreas but act in liver

temperature regulation: too hot

* skin hair rise
* vasodilation: arterioles expand, allowing more blood to flow near to the skin
* sweat gland produces sweat

temperature regulation: too cold

* skin hair flatten
* vasoconstriction: arterioles constrict, less blood flow through capillaries near skin
* sweat gland stops producing sweat

gravitropism

response in which plants grow towards or away from gravity

phototropism

response in which plants grow away to towards the direction light is coming

growth hormone in plants

auxin

function of growth hormone in plants

* made in tips of shoots
* control tropisms
* move to where it is required
* causes plant cells to elongate

how phototropism works

* auxin is made in tips of shoots only
* auxin moves downwards and away from light
* auxin causes cell elongation
* when 1 side grows longer than the other, it causes the shoot to bend towards light

B8: Gas exchange & Respiration

inhalation

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* ribcage rise upwards & outwards
* diaphragm contract & flatten
* lung volume increase
* air flows outside to inside

exhalation

* ribcage falls downwards and inwards
* diaphragm relax and curve upwards
* lung volume decreases
* air flows inside → outside

inspired air

* nitrogen: 79: not used and produced by any body processes
* oxygen: 21: used in repiration
* carbon dioxide: 0.04
* water vapour: variable
* temperature: room temp

expired air

* nitrogen: 79
* oxygen: 16
* carbon dioxide: 4: produced in respiration
* water vapour: saturated: produced in respiration, evaporates from surface of alveoli
* temp: 37

adaptations of alveoli

* large surface area: maximise absorption as more gas molecules can diffuse at the same time
* thin: only 1 cell thick, short diffusion distance, faster rate of absorption
* covered with blood capillaries: good blood supply, gas diffuse in and out of blood
* good ventilation with air: maintain high concentration gradient of oxygen and carbon dioxide

specialised cells

* goblet cells: produce mucus to trap pathogens and dust particles
* ciliated epithelial cells: tiny hairs sweep mucus out of the lungs and up the throat
* found in trachea and bronchi

effects of breathing during exercise

* increase rate of breathing
* increase depth of breathing

effect of physical exercise on breathing

* during exercise, muscles need more energy, which results in more respiration, and more carbon dioxide produced
* carbon dioxide dissolve into blood and turn into carbonic acid→ makes blood acidic
* brain receptors detect blood pH level, and send nerve signals to lung muscles
* lung muscles would contract and relax faster→ increase breathing rate

diseases that smoking may cause

lung cancer, COPD

symptoms of COPD

difficulty in breathing, permanent lung damage

effects of dangerous chemicals produced by smoking

* nicotine: additive; narrow blood vessels, increase blood pressure, increase risks of coronary heart disease
* carbon monoxide: bind permanently with hemoglobin in RBC→ less oxygen supply for respiration
* tar & smoke particles: lung cancer; chronic bronchitis: inflammation and excess mucus due to damaged cells; emphysema: alveoli walls destroyed→ reduce surface area for diffusion

definition of aerobic respiration

chemical reactions in cells that use oxygen to break down nutrient molecules and release energy

equation of aerobic respiration

glucose + oxygen → carbon dioxide + water

why do cells need to produce energy

* grow/reproduce
* muscle contraction
* body temperature regulation

anaerobic respiration

chemical reactions in cells that break down nutrient molecules to release energy without using oxygen

use of anaerobic respiration

* yeast anaerobic respiration: glucose→ ethanol + carbon dioxide
* muscle cells: glucose→ lactic acid + energy

anaerobic respiration in bread making

produce carbon dioxide that is trapped in the dough to make the dough soft and spongy

oxygen debt

oxygen supply less than oxygen demand

repaying oxygen debt

* during vigorous exercise, lactic acid build up in muscles and blood, causing oxygen debt
* after exercising, we continue to have high breathing rate to have extra oxygen → break down lactic acid in liver

B7: Transport in plants & mammals

xylem

hollow tubes that run through roots, stem and to the lead, made from dead cells

role of xylem

transports water from the roots to leaves

role of phloem

transports sucrose & amino acids from areas where they are produced to areas where they are stored

root hair cells

* function: absorb water and minerals
* adaptation: they are many, have large surface area that increase rate of absorption

water uptake of plants

* water first enter the root hair cells by osmosis
* water crosses cortex of the root, cell by cell via osmosis
* until it reaches xylem
* water is then pulled up to stem and leaves through xylem vessels
* water diffuses into mesophyll cells of leaves

transpiration(definition)

the loss of water vapour in plant leaves, by evaporation of water at the surface of mesophyll cells, followed by diffusion of water vapour into stomata

water is able to continuously flow up the plant due to

* transpiration pull: the loss of water vapour in the leaves creates a tension that pulls water molecules up and maintain high water potential gradient
* cohesion of water molecules: the water molecules tend to stick together and do not break apart, this helps to draw up a continuous column of water through xylem

factors affect transpiration rate

* temperature: as temperature increases, water evaporates from the leaves faster, therefore rate of transpiration is increased
* humidity: rate of transpiration is inversely proportional to humidity; the higher the humidity, the less steep the water potential gradient between inside and outside leaves, therefore rate of transpiration is slower

translocation

the movement of sucrose and amino acids in phloem from regions of production to regions of storage or where they are used

double circulatory system

blood passes heart twice in 1 circuit, 1 goes to lungs, 1 goes to the body

advantages of double circulatory system

* separate oxygenated and deoxygenated blood

blood vessels flow to: liver

hepatic vein & hepatic artery

blood vessels flow to: kidney

renal vein & renal artery

blood vessel flow from stomach to liver

hepatic portal vein

blood vessel from head & arms to heart

superior vena cavab

blood vessel from body to heart

inferior vena cava

blood vessel from heart to body

aorta

cardiac cycle

* atria contracts, pressure in atria increases, blood is pushed into ventricle (atrioventricular valves open)
* ventricle contracts, atrioventricular valves close, semilunar valves open; blood is pushed out to the lungs and the body
* heart relax and is filled with blood, semilunar valves close

artery

* carries blood from heart to tissues
* thick walls: withstand high pressure of blood & prevent blood vessels from bursting
* small lumen: maintain high pressure
* elastic wall: allow blood vessel to expand & recoil as blood pushes through

vein

* have valve: prevent backflow of blood
* big lumen: reduce resistance to blood flow
* thin walls: maintain blood at low pressure

capillaries

* very small lumen
* 1 cell thick
* highly branched

blood contents

* RBC
* WBC
* platelets
* plasma

red blood cells

* carries oxygen
* contains hemoglobin
* no nucleus: to fit in as much hemoglobin as possible
* bi-concave shape: increase surface area for diffusion of oxygen

white blood cells

* phagocytes: remove any microorganism enter body through phagocytosis
* lymphocytes: produce bacteria

plasma

mostly water, contains many dissolved substances

platelets

* help to clot blood and close wound
* activated when blood vessels are damaged

effect of physical exercise on pulse rate

* more glucose and oxygen needed for respiration to release energy
* breathing rate increases to send oxygen to cells
* heart pumps faster to send oxygen and glucose around the body

coronary heart disease: factors increase risks

* diet high in fats
* poor lifestyle
* genetic factors
* old age

coronary heart disease: the cause

* coronary artery supplies blood to the heart muscle
* plaque builds up in arteries
* plaque explodes→ blood clot forms
* blood clot blocks blood flow
* heart muscle die→ heart attack

B1: Characteristics of living things

Movement

an action done by an organism that causes a change in position or place

respiration

chemical reactions that break down nutrients to release energy for metabolism

sensitivity

the ability to sense or detect stimuli in the internal or external environment to make appropriate responses

growth

the permanent increase in size and dry mass by increasing cell size or cell number

reproduction

the process of making more of the same kind of organism

excretion

the passing out of waste materials from metabolism, toxic substances in excess of the body

nutrition

the taking in of materials for energy, growth and development

B6: Animal Nutrition

balanced diet

a diet that contains all nutrients in correct proportions

factors affect dietary needs

* age
* gender
* active lifestyle

carbohydrate

* source: bread, rice, pasta
* function: provide energy to body
* malnutrition: too much carbohydrate: diabetes; too little: marasmus

protein

* source: fish, meat, tofu
* function: growth & repair
* malnutrition: kwashiorkor: stunted growth

fats

* source: oil, butter, cheese
* function: store energy, keep body warm
* malnutrition: cardiovascular disease, obesity

vitamin C

* source: citrus fruits
* function: make collagen
* malnutrition: scurvy - bleeding gum, joint pain, skin wounds

vitamin D

* source: sunlight, fish oil, egg yolk
* function: absorb calcium
* malnutrition: rickets: weak & soft bones

calcium

* source: dairy products, soy beans
* function: strengthen bones
* malnutrition: rickets

iron

* source: red meat, spinach
* function: make hemoglobin
* malnutrition: anemia: dizzy, pale skin

fibre

* source: fruits & vegetables
* function: help stretch muscles in the gut and push food along intestine
* malnutrition: constipation

water

* function: hydration, medium for blood transport, regulate body temp
* malnutrition: dehydration