Control, Response and Homeostasis

• Too cold- Erector muscles contract, this traps an insulating layer of air. Shivering, needs respiration which transfers some energy to warm the body. Very little sweat is produced.
• Vasoconstriction- blood vessels near the surface of the skin constrict, which means less blood flows near the surface so less energy is transferred to the surroundings.
• Vasodilation- Increased blood flow to the skin, which increases the rate of heat loss to the surroundings.
• Too hot- Erector muscles relax so hair lies flat, lots of sweat is produced. When sweat evaporates, it cools the body by transferring energy into the environment.
• Homeostasis is the maintenance of a constant internal environment.
• Iris- Muscles that alter the size of the pupil to control the amount of light entering
• Sclera- Protective, tough white outer coat
• Blind Spot- where the optic nerve leaves the eye, there are no light sensitive cells here
• Optic Nerve- Carries impulses from the retina to the brain
• Cornea- clear part of the sclera. Refracts light.
• Pupil- Hole in the centre of the iris which allows light to enter
• Choroid- absorbs light to prevent reflection, also contains blood vessels
• Reflex responses are always rapid, automatic and generally protective
• Diabetes- a condition where you are unable to control your blood glucose levels. In type 1, the body does not release insulin. In type 2, the body cells do not respond to the chemical signal from insulin.
• Glucose in urine is a symptom of diabetes, it can be detected by a Benedict's test
• Diabetes treatment- Injecting insulin, transplant of healthy pancreatic tissue and low carb/sugar diets
• A tropism is a growth response in a plant to a one directional stimulus. It is caused by the hormone auxin.
• Positive phototropism- growth towards light
• Positive gravitropism- root growth down into the ground, with gravity
• Sense organs are groups of receptor cells which respond to specific stimuli: light, sound, touch, temperature, chemicals and then relay this information as electrical impulses along neurones to the central nervous system.
• Retina – light sensitive layer , an image is formed here, impulses sent to optic nerve.
• Metabolism operates only within a narrow range of temperature and pH and requires appropriate nutrients and water.
• Benedict's solution turns from blue to brick red in the presence of glucose. It must be heated strongly or boiled first.
• Negative Feedback- Any change from the balance in optimal internal conditions results in the body's hormonal and nervous systems compensating for the change and restoring the balance.
• Diabetes Symptoms- Glucose in urine, thirst, low insulin levels
• Examples of reflexes- withdrawal reflex, blinking and pupil size
• The CNS coordinates the response- it decides how to react to the stimulus. Electrical impulses then travel along neurons to an effector (muscle or gland)- a muscle could contract or a gland may secrete a hormone.
• The junction between two neurons is called a synapse. The nerve impulse is transferred by chemicals which diffuse along the gap.
• Lens – changes shape to focus light onto retina
• Hormones- proteins which are chemical messengers, carried by the blood, and control many body functions
• When the blood glucose level rises, the pancreas releases the hormone insulin, a protein, into the blood, which causes the liver to reduce the glucose level by converting glucose to insoluble glycogen and then storing it.
• Causes of diabetes- genetics, obesity, age, and lifestyle choices such as lack of exercise
• Negative alcohol effects- slows reaction time, liver disease, increased blood pressure, circulatory and heart disease and withdrawal symptoms.
• Drugs- circulatory and heart disease, mental health problems, withdrawal symptoms. Soft drugs include cannabis. Hard drugs include heroin and ecstasy- these are typically more dangerous.
• The food we eat has a crucial impact on how we function. Eating too much can lead to obesity, which links to type 2 diabetes. This is because it makes the body less sensitive or resistant to insulin, so it struggles to control the concentration of glucose.