Organism level systems Revision Notes

How Hormonal Contraception Works

Hormonal contraceptives contain synthetic oestrogen and/or progesterone. These hormones primarily work by inhibiting the release of an egg from the ovary (ovulation), effectively preventing it from happening. They also thicken the cervical mucus, creating a barrier that makes it difficult for sperm to travel through the cervix and reach an egg. Additionally, hormonal contraception can alter the lining of the uterus, making it thinner and therefore less suitable for a fertilised egg to implant. Different hormonal methods, like pills, injections, or implants, vary in their hormone dosages, duration of effect, and administration frequency.

Types of Hormonal Contraception and Their Characteristics

Common hormonal methods include the combined oral contraceptive pill (containing oestrogen and progesterone), which is highly effective but requires daily use. The progesterone-only pill (mini-pill) works similarly, but without oestrogen side effects. Other examples are the contraceptive injection (effective for 8-13 weeks), the contraceptive implant (lasts up to 3 years), and the contraceptive patch (changed weekly). Advantages often include high effectiveness and not interrupting sex. Disadvantages can include potential side effects like mood changes, headaches, weight changes, and no protection against sexually transmitted infections (STIs).

Types of Non-Hormonal Contraception and Their Characteristics

Non-hormonal contraceptives do not use hormones. Barrier methods like male and female condoms physically block sperm from reaching the egg. Male condoms are the only method that also offers significant protection against STIs. Diaphragms and cervical caps are also barrier methods, used with spermicide. The copper Intrauterine Device (IUD) is a long-acting reversible contraceptive that works by releasing copper, which is toxic to sperm and eggs, preventing fertilisation and implantation. Advantages of non-hormonal methods include no hormone-related side effects and, for condoms, STI protection. Disadvantages include user error affecting effectiveness (for barrier methods) and IUD insertion procedures.

Evaluating Contraceptive Methods

When evaluating contraception, factors such as effectiveness, potential side effects, ease of use, duration of protection, and protection against STIs are considered. Hormonal methods are generally highly effective at preventing pregnancy but do not protect against STIs. They can have systemic side effects. Non-hormonal methods like condoms offer STI protection but can be less effective if not used correctly. Long-acting methods (e.g., IUD, implant, injection) remove the need for daily or weekly action, increasing their typical effectiveness. The choice of contraception depends on individual health, lifestyle, and needs.

Auxins and their Commercial Applications (Higher)

Auxins are plant hormones primarily involved in cell elongation. They are used extensively to promote root formation in plant cuttings, allowing for vegetative propagation. This is achieved through rooting powders or gels containing synthetic auxins. Another significant application is as selective weed killers; high concentrations of synthetic auxins cause broad-leaved plants (dicots) to grow uncontrollably and die, while narrow-leaved plants (monocots) like cereals are unharmed. Auxins are also used to prevent fruit drop by delaying the formation of the abscission layer, ensuring fruits remain on the plant longer for optimal ripening and harvest.

Gibberellins: Functions and Agricultural Uses (Higher)

Gibberellins are a group of plant hormones that stimulate stem elongation, promote seed germination, and influence flowering and fruit development. Commercially, gibberellins are used in the brewing industry to speed up the malting process for barley, converting starch into maltose more rapidly. They are also applied to switch seeds from dormancy to germination, an important technique in agriculture. Furthermore, gibberellins can be used to increase the size of fruits, particularly in grapes, by promoting cell enlargement and elongation of the flower stalk, leading to larger, more widely spaced berries.

Ethene: Role in Ripening and Abscission (Higher)

Ethene (ethylene) is a gaseous plant hormone that plays a key role in fruit ripening and senescence (ageing) of plant tissues, including flower and leaf abscission. Its most common commercial application is in controlling fruit ripening. Fruits like bananas and tomatoes are often harvested unripe to facilitate transportation and extend shelf life. Upon reaching their destination, they are exposed to ethene gas in controlled environments, which triggers the ripening process, making them marketable when needed. Ethene is also involved in promoting the shedding of leaves and fruit (abscission), although this effect is less commonly exploited commercially for cultivation compared to ripening.

Summary of Plant Hormone Uses (Higher)

In summary, plant hormones are crucial for plant growth and development, and their synthetic analogues are widely used in horticulture and agriculture. Auxins are used for rooting cuttings, selective weed killing, and preventing fruit drop. Gibberellins accelerate malting, break seed dormancy, and increase fruit size. Ethene is primarily employed to ripen fruits post-harvest. These applications allow for precise control over plant characteristics, improving yield, quality, and market timing.

Components of the Nervous System

The nervous system is divided into two main parts: the Central Nervous System (CNS) and the Peripheral Nervous System (PNS). The CNS consists of the brain and spinal cord, which are responsible for processing information and coordinating responses. The PNS comprises all the nerves outside the brain and spinal cord, acting as a communication pathway between the CNS and the rest of the body. Key components include sensory receptors that detect stimuli, sensory neurons that transmit impulses to the CNS, interneurons within the CNS for processing, motor neurons that carry impulses from the CNS, and effectors (muscles or glands) that carry out responses.

Pathway of a Coordinated Response

A coordinated response begins with a stimulus being detected by sensory receptors. These receptors convert specific stimuli (e.g., light, pressure, temperature) into electrical impulses. Sensory neurons then transmit these impulses from the receptors towards the Central Nervous System (CNS). In the CNS (brain or spinal cord), interneurons process the information. The CNS integrates these signals to formulate an appropriate response. Motor neurons then carry the electrical impulses from the CNS to effector organs, which are muscles or glands. Muscles contract to produce movement, while glands secrete substances like hormones, leading to a coordinated action or response.

The Role of Neurons

Neurons (nerve cells) are the fundamental units of the nervous system, specialised for transmitting electrical signals. Sensory neurons detect stimuli and send impulses from receptors to the CNS. Interneurons are found entirely within the CNS and are responsible for connecting sensory and motor neurons, enabling complex processing and decision-making. Motor neurons transmit impulses from the CNS to effectors (muscles or glands), causing them to respond. This chain of communication ensures rapid and efficient signal transmission throughout the body, allowing for quick reactions to environmental changes and maintenance of internal conditions.

Gross Structure of the Kidney

The kidneys are bean-shaped organs positioned on either side of the spine. Each kidney is enclosed by a renal capsule. Internally, the kidney is organised into two main layers: the renal cortex (the outer layer) and the renal medulla (the inner layer). The medulla contains renal pyramids, which are cone-shaped tissues. Urine collects in the renal pelvis, a central basin, before being transported out of the kidney by the ureter.

Components of a Kidney Tubule (Nephron)

The functional unit of the kidney is the nephron, also known as the kidney tubule. Each nephron starts with the Bowman's capsule, a cup-like structure encasing the glomerulus (a capillary network). The Bowman's capsule leads into the renal tubule, a long, coiled tube. The renal tubule consists of distinct sections: the proximal convoluted tubule, the loop of Henle, and the distal convoluted tubule.

Functions of Kidney Tubule Sections

Within the nephron, specific functions occur at different points. The Bowman's capsule and glomerulus are sites of initial blood filtration. The proximal convoluted tubule is where the majority of useful substances, such as glucose and amino acids, are reabsorbed back into the blood. The loop of Henle is important for establishing an osmotic gradient that aids in water reabsorption. The distal convoluted tubule has a role in regulating water and ion balance. Finally, multiple nephrons empty their filtered contents into collecting ducts.