Unit 1 Biology - AoS 2

Levels of structural organisation

Cells, tissues, organs, systems, organisms

Parenchyma cells

The major cells of plants, responsible for photosynthesis and other metabolic activity.

Sclerenchyma cells

Protects seeds and support the plants

Collenchyma cells

Provide flexible and mechanical support; found in stems and leaves

Xylem cells

Cells of the xylem are responsible for the transport of water and minerals from the roots to the leaves of the plant.

Phloem cells

Cells of the phloem are responsible for the transport of sugars and other nutrients throughout the plant.

Dermal tissue

The protective covering of plants which secrete a waxy film to form a barrier between the plant and the environment to reduce water loss and damage

Ground tissue

Make up the majority of the interior of the plant and carry out metabolic functions. Vascular tissues run through the ground tissue of vascular plants, carrying water and nutrients.

Leaves

Sites of gas exchange and responsible for photosynthesis. In most species, leaves are organised to increase sunlight exposure.

Flowers

The sexual reproductive organs of flowering plants (angiosperms). Following the fertilisation of male and female gametes which are contained in pollen, seeds develop and the ovary of a flower grows into a fruit.

Fruits

Grown from a flower post-fertilisation. Fruits protect seeds and are often specialised to attract animals that aid with seed dispersal.

Stems

Support the leaves, flowers, and fruits, as well as transport water and nutrients between the roots and shoots.

Roots

Absorption and storage of water and nutrients from the soil. Roots are also responsible for anchoring the plant to the ground and providing structural support.

Root system

The root system is typically underground. It absorbs water and nutrients from the soil and provides the plant with support and structure.

Shoot system

The shoot system of angiosperms is made up of the reproductive and non-reproductive sections. The reproductive sections include the flowers and fruit, and the non-reproductive sections include the leaves and stems.

What do vascular tissues in plants do?

They transport water from the roots to the leaves of a plant, and glucose and nutrients throughout the plant

Xylem tissue

Tubes that transport water, and minerals such as potassium, nitrogen, and phosphorus in one direction from the roots to the leaves of a plant

Phloem tissue

Tubes that transport sugars and other nutrients around a plant in both directions.

Transpiration stream

The uninterrupted stream of water and solutes which is taken up by the roots and transported via the xylem to the leaves where it evaporates into the air/apoplast-interface of the substomatal cavity.

What does transpiration help plants with?

Apart from assisting photosynthesis, transpiration helps plants regulate heat and water balance, distribute nutrients throughout the plant, and prevent wilting and cell damage.

Environmental factors that affect transpiration rates

Temperature, light, humidity, wind, water availability

What do guard cells do?

Regulate transpiration

Guard cell

A pair of curved cells that surround a stoma. When hot they lose turgor pressure and become flaccid, closing the stomata to limit water loss

Translocation

The movement of substances from a source to other tissues in the plant via the phloem.

Translocation of sugars

Sugars produced in sources, such as leaves, need to be delivered to growing parts of the plant via the phloem in a process called translocation, or movement of sugar. The points of sugar delivery, such as roots, young shoots, and developing seeds, are called sinks.

What is the purpose of the excretory system?

The purpose of the excretory system is to remove excess and unwanted substances from the body and to maintain a stable internal environment.

Capsule (of kidney)

Outer membrane covering kidney

Cortex

Outermost tissue of kidney that contains nephrons

Medulla

Second striated layer - tubes carrying filtered wastes to centre of kidney (site of loop of Henle)

Nephron

Nephrons basic functional unit of kidneys - filtration and reabsorption

200,000 to 2 million

Regulation of body fluids within narrow limits

Blood from body flows into tight clusters of capillaries known as glomerulus in each nephron

Glomerulus and Bowman's capsule

The Bowman's capsule forms a thin walled container around the glomerulus - where blood enters the tubule

The other end of the tubule connects to the collecting duct to carry filtrate to the ureter

Loop of Henle

The loop of Henle are the section of the nephron tubule that extend in a u-shape into the medulla giving it the striated appearance

Peritubular capillaries

Arterioles leaving the glomerulus form an additional capillary network around the tubules

Here the exchange of materials between the bloodstream and filtrate in the tubules takes place - reabsorption and secretion

Ultrafiltration

When particles being separated are very small eg. molecules or ions

Steps of ultrafiltration

1. Blood in glomerulus is under high pressure. Like all capillaries, the walls of the glomerulus have pores.

2. Membrane lining Bowman's capsule also has pores. The pressure inside the glomerulus forces small particles from the blood into the Bowman's capsule.

Ultrafiltrate

The mixture of small molecules inside the Bowman's capsule which contains mainly water with dissolved amino acids, glucose, mineral salts, and urea

Selective reabsorption

The absorption of certain selected molecules back into the blood from the fluid in the nephron tubule.

What does the loop of Henle do?

Increases the salt content of the tissues of the medulla

This helps in the reabsorption of water from the ultrafiltrate in the distal tubules and collecting ducts.

Hypothalamus

A small region in the brain that helps maintain body temperature and often influences the function of the pituitary gland

Pancreas

An organ that sits across the back of the abdomen that is involved in the functioning of the digestive system and maintenance of blood glucose levels by releasing insulin and glucagon

Insulin

A hormone produced by the pancreas or taken as a medication by many diabetics which regulates blood glucose levels

Homeostasis

The maintenance of a relatively stable internal environment in the body despite changes in the external environment

Stimulus-response model

Stimulus, receptor, modulator, effector, response

Negative feedback

A negative feedback loop occurs in biology when the product of a reaction leads to a decrease in that reaction. In this way, a negative feedback loop brings a system closer to a target of stability or homeostasis.

Homeothermy

Thermoregulation that maintains a stable internal body temperature regardless of external influence

Poikilothermy

The quality of having a body temperature that varies or fluctuates, depending on the temperature of the environment; cold-bloodedness

Negative feedback loop - increased temperature

Stimulus - increased temperature

Receptor - thermoreceptors

Modulator - hypothalamus

Effectors - sweat glands, blood vessels in skin, cerebral cortex, arrector pili muscles, ells

Response - sweating, dilation of arterioles, change in behaviour, flattening of hair, decrease in metabolic rate

Negative feedback loop - decreased temperature

Stimulus - decreased temperature

Receptor - thermoreceptors

Modulator - hypothalamus

Effector - skeletal muscle cells, blood vessels in skin, cerebral cortex, arrector pili muscles, cells, brown fat

Response - shivering, constriction of arterioles, change in behaviour, lifting of hair, increase in metabolic rate, burning of triglycerides

Glycogen

Storage form of glucose

Glycogenesis

The process of creating glycogen from glucose

Glycogenolysis

The process of breaking down glycogen into glucose

Negative feedback loop - increased blood glucose

Stimulus - blood glucose above 5 mmol/L

Receptor and modulator - Islets of Langerhans - beta cells secrete insulin

Effector - skeletal muscle and fat cells, liver cells

Response - increased uptake of glucose via insertion of glucose transporters into cell membrane, increased conversion of glucose into glycogen

Negative feedback loop - decreased blood glucose

Stimulus - blood glucose below 5 mmol/L

Receptor and modulator - Islets of Langerhans - alpha cells secrete glucagon

Effector - liver cells

Response - breakdown of glycogen into glucose which is released into the blood stream

Negative feedback loop - decreased water levels

Stimulus - decrease in water levels

Receptors - baroreceptors detect fall in blood pressure and volume, osmoreceptors detect increases in osmolality

Modulators - release of renin from kidney cells causing release of aldosterone, hypothalamus causes release of ADH from posterior pituitary gland

Effector - activation of sodium-potassium pumps increasing reabsorption of sodium, aquaporins inserted into the distal convoluted tubule and collecting duct of kidneys, stimulation of cells in thirst centre

Response - increased reabsorption of water from kidney filtrate, increase in consumption of fluid

Type 1 diabetes

An autoimmune disease that usually develops during childhood or adolescence and is characterized by a severe deficiency of insulin, leading to high blood glucose levels.

Cause of type 1 diabetes

Beta cells in pancreas recognised as non-self and attacked by autoantibodies. Alpha cells are also damaged.

Type 2 diabetes

Diabetes of a form that develops especially in adults and most often obese individuals and that is characterized by high blood glucose resulting from impaired insulin utilisation coupled with the body's inability to compensate with increased insulin production.

Hyperthyroidism

Hyperthyroidism (overactive thyroid) occurs when your thyroid gland produces too much of the hormone thyroxine. Hyperthyroidism can accelerate your body's metabolism, causing unintentional weight loss and a rapid or irregular heartbeat.

Hypothyroidism

Hypothyroidism is a condition where there isn't enough thyroid hormone in your bloodstream and your metabolism slows down.