Comprehensive Study Guide: Transport in Plants and Mammals

Transport Systems in Plants

Overview of the Plant Transport System: - The system is composed of two primary tissues: Xylem and Phloem. - The Phloem is responsible for the transport of sucrose and amino acids. - The Xylem is responsible for the transport of water and mineral ions.
Structure of Xylem: - Consists of a long chain made of many hollow, dead cells joined end-to-end to form an open tube. - Xylem vessels contain no cytoplasm or nuclei. - The cell walls are thickened majorly with Lignin. - Lignin is a very strong substance that helps in keeping plants upright.
Structure of Phloem: - Phloem tubes are made of many cells joined end-to-end. - Their end walls have not completely broken down; instead, they form sieve plates, and the cells are called sieve tube elements. - Sieve tube elements contain cytoplasm but possess no nucleus. - Phloem cell walls do not contain lignin. - Companion cells are located alongside sieve tubes and contain the nucleus for the phloem tissue.

Functions and Directionality of Plant Transport

Xylem Functions: - Transports water and mineral ions ( $Mg^{2+}$ , etc.). - Roots absorb water and mineral ions from the soil. - Water enters the root and travels up through the xylem to the leaves, flowers, and fruits. - Direction of transport is strictly unidirectional: from the roots, via the stem, to the leaves.
Phloem Functions: - Transports sucrose, amino acids, and hormones throughout the plant. - Sucrose is a soluble complex sugar specifically made for transporting energy. - These substances are made in the leaves through photosynthesis or mobilization of starch in storage organs. - Direction of transport is bidirectional: - Downwards: From leaves to roots. - Upwards: From leaves to flowers or buds. - Hormones control activities such as cell division.

Anatomy of Roots and Stems

Transverse Section of a Root: - Cortex: Stores food as starch. - Root tip: Contains cells that can divide as the root grows through the soil. - Root cap: Protects the root tip as it grows. - Stele components: Includes the Xylem (inner star-shape), Phloem (outer areas), and the Endodermis.
Transverse Section of a Stem: - Vascular Bundle: Arranged in a group of Xylem, Phloem, and Cambium. - Cambium: Found between the xylem and phloem. It is the tissue that makes new xylem and phloem as the plant grows. - Epidermis: The outermost protective layer. - Cortex: Outer layer of tissue below the epidermis. - Pith: The central region of the stem.

Mechanism of Water and Mineral Uptake

Root Hair Cells: - Function to anchor the plant into the soil and absorb water. - Water passes into root hairs by osmosis. - Adaptation 1: They have thin, permeable cell walls which provide a large surface area for absorption. - Adaptation 2: The cell sap is more concentrated than the soil water. - The cell membrane is partially permeable, allowing water to diffuse from the soil into the root hair. - Water passes across the root cortex by osmosis before entering the xylem and then ascending the stem to the leaves.
Mineral Uptake: - Minerals are absorbed by active transport, which uses energy produced by respiration.
Movement Mechanisms: - Cohesion: The tendency of water molecules to stick to each other. - Adhesion: The tendency of water molecules to stick to the walls of the xylem vessels. - Water is pulled up the xylem vessels in the stem from the roots to the leaves by a transpiration pull.

Transpiration and Leaf Processes

Definition of Transpiration: - It is the evaporation of water from the surfaces of mesophyll cells in the leaves followed by the diffusion of water vapor through the stomata into the atmosphere.
Evaporation Mechanism: - Water evaporates from the surfaces of the mesophyll into the air spaces. - The cell wall has the highest water potential. - There is typically more water vapor in the intercellular air spaces than in the air outside the leaf. - Water vapor diffuses through the stomata into the atmosphere.
Stomatal Regulation: - More transpiration takes place during the day than at night because stomata are open during the day to allow Carbon Dioxide ( $CO_2$ ) to diffuse in for photosynthesis. - Stomata may close to reduce the rate of water loss. - In hot and dry conditions, stomata may close to prevent wilting.
Wilting and Recovery: - If the plant does not get enough water, it will wilt. - Cells lose turgor and become flaccid. - Leaves move downwards so they are not directly exposed to heat. - When the temperature decreases, the plant can absorb more water than it loses by transpiration, allowing the leaves to recover.

Factors Affecting Transpiration and Measurement

Light Intensity: - Increased light intensity causes stomata to open, increasing the rate of transpiration.
Humidity: - Lower humidity creates a steeper concentration gradient for water vapor between the leaf and the atmosphere. - In dry conditions where humidity is low, the rate of transpiration is high.
Temperature: - As temperature increases, water molecules on the leaves have more kinetic energy and enter the air instead of the leaf.
Measuring Transpiration (The Potometer): - A potometer is used to measure the rate of water uptake, which is used to estimate the rate of transpiration. - The volume of water absorbed is measured against time. - A small bubble is allowed to form in the capillary tube; the distance moved by the bubble is a measure of the rate of water uptake.

Translocation of Nutrients

Definition: - Translocation is the movement of sucrose and amino acids through the phloem from regions of production (Sources) to regions of storage or utilization (Sinks).
Sources and Sinks: - Source: Where food is produced (e.g., leaves during photosynthesis). - Sink: Other parts of the plant where food is used or stored (e.g., roots, fruits, or shoot tips for growth). - Sucrose and amino acids are used in respiration, broken down to give simpler sugars, or changed to starch for storage in the root cortex or leaves. - Sucrose can be stored in some fruits to make them sweet and attract animals. - Unlike xylem (unidirectional), phloem has bidirectional movement.

Transport in Mammals: The Circulatory System

The Heart and Blood Vessels: - The heart is a pump that circulates blood through blood vessels. - Blood flows in arteries away from the heart at high pressure. - Blood flows in veins towards the heart at low pressure. - Smallest blood vessels are known as capillaries, which connect arteries and veins.
Capillary Function: - Beds of capillaries ensure organs receive a good supply of Oxygen ( $O_2$ ) and remove Carbon Dioxide ( $CO_2$ ) and other waste products. - Arteries branch into smaller muscular vessels called arterioles to reduce pressure before blood enters capillaries. - High blood pressure could damage the thin-walled capillaries. - After passing through capillaries, blood pressure is even lower.
Valves: - Semi-lunar valves ensure that blood does not flow backwards.
Circulation Types: - Fish: Have a single circulation system where blood flows through the heart once in one circuit around the body. - Mammals: Have a double circulation system where blood flows through the heart twice in one circuit.

The Mammalian Heart: Structure and Function

Heart Chambers: - The heart is divided into the Left Side and the Right Side by a wall of muscle called the Septum. - Atria: Upper chambers (Left Atrium and Right Atrium). - Ventricles: Lower chambers (Left Ventricle and Right Ventricle). - Ventricles have much thicker walls because they must pump blood out to the body, requiring more strength.
Vessel Connections: - Vena Cava: The vein that brings deoxygenated blood from the body to the right atrium. - Aorta: The artery that carries oxygenated blood from the left ventricle to the rest of the body. - Pulmonary Vein: Carries oxygenated blood from the lungs to the left atrium. - Pulmonary Artery: Carries deoxygenated blood from the right ventricle to the lungs.
Valves and Support: - Valves (atrio-ventricular and semi-lunar) ensure one-way flow. - Tendons support the valves during contraction.

Cardiac Mechanics and the Heartbeat Cycle

The Cardiac Cycle: - Relaxation (Diastole): The heart muscle relaxes, the heart becomes larger, and blood flows into the atria. Semi-lunar valves are shut. - Atrial Contraction: Muscles of the atria contract while ventricle muscles remain relaxed. Blood is forced into the ventricles through the atrio-ventricular valves. - Ventricular Contraction (Systole): Ventricle muscles contract. This pressure forces the atrio-ventricular valves shut. Blood is forced out into the arteries through the semi-lunar valves. Atria muscles relax during this phase.
The Pacemaker: - The pacemaker (sinus node) sends electrical signals through the heart wall at regular intervals, making the heart contract. - The heart rate is monitored and adjusted by the brain. - Brain signals are sent along nerves to the pacemaker.
Exercise and Heart Rate: - During exercise, muscles respire more quickly to release energy for movement. - This produces more $CO_2$ which dissolves in the blood. - Receptor cells sense the drop in $pH$ caused by $CO_2$ and trigger the pacemaker to increase the heart rate.

Coronary Heart Disease (CHD) and Health

Definition: - Blockage of the coronary arteries is called Coronary Heart Disease (CHD). - Coronary arteries are found on the outside of the heart and supply blood directly to the heart muscles.
Mechanism of Heart Attack: - The heart requires a constant supply of nutrients and $O_2$ for contraction and relaxation. - If a coronary artery gets blocked (e.g., by a blood clot), cardiac muscles are short of oxygen and can no longer contract. - This leads to a heart attack.
Risk Factors for CHD: - Smoking. - Diet (high fat/cholesterol). - Obesity. - Stress. - Heredity factors.
Pulse Rate: - A pulse is caused by the expansion of an artery due to blood being forced through by the heart. - Pulse rate is equivalent to heart rate.

Characteristics and Structure of Blood Vessels

Arteries: - Carry blood away from the heart. - High pressure. - Thick layer of muscles and elastic tissue. - Small lumen. - Smooth lining to facilitate flow.
Capillaries: - Arise from repeated division of arteries. - Walls are only one cell thick and very thin. - No muscle or elastic tissue. - Facilitate gas and nutrient exchange. - Pressure is low to allow contact with tissues.
Veins: - Formed from joined capillaries. - Carry blood towards the heart. - Low pressure. - Relatively thin walls compared to arteries (less muscle/elastic tissue). - Wide lumen to offer less resistance to flow. - Contain valves to prevent backflow.

Composition and Components of Blood

Plasma: - The liquid part of the blood. - Transports: Glucose, Mineral ions, Hormones, Carbon Dioxide ( $CO_2$ ), Urea, and Antibodies.
Red Blood Cells (RBCs): - Biconcave discs with no nucleus. - Provides a large surface area. - Contain Hemoglobin, a protein containing iron. - Function: Transport oxygen and some $CO_2$ . They are flexible to squeeze through tiny capillaries.
White Blood Cells (WBCs): - Variable shapes with a nucleus. - Can squeeze through capillary walls to reach and destroy pathogens (foreign bodies that cause disease). - Phagocytes: Digest bacteria in a process called phagocytosis. - Lymphocytes: Produce antibodies.
Platelets: - Small cell fragments with no nucleus. - Responsible for blood clotting, which prevents pathogens from entering the body and prevents excessive blood loss.

Specific Organ Circulation and Specialized Functions

Organ-Specific Vessels: - Kidney: Renal artery (in) and Renal vein (out). - Liver: Hepatic artery (in) and Hepatic vein (out). - Note: Hepatic portal vein (connects intestine to liver) was also mentioned.
Stability of Hemoglobin: - Oxyhemoglobin is described as unstable, allowing it to release oxygen easily to tissues.