Importance of Water

Importance of Water • It acts as: • solvent / reaction medium • medium for transport (e.g. blood) • metabolite (e.g. photosynthesis) • others like act as cooling agent (e.g. sweating in hot weather) • as supporting agent (e.g. turgidity in young plant) • for sexual reproduction

Water as a Solvent • dissolve most organic and inorganic substances • needed for all biochemical reactions • remove excretory products such as urea and excess salts • in plants, root hairs absorb mineral salts present in soil in solution form

Water as a Medium of Transport • human blood plasma consists mainly of water (90%) • carry many dissolved substances like excretory wastes, hormones and gases around the body • in plants, sugar and mineral salts are transported in solution in vascular bundles

Water as a Metabolite • in plants during photosynthesis, carbohydrates are synthesized from carbon dioxide and water • essential in hydrolytic reactions, e.g. digestion

Ways of Gaining Water in Animals • drinking • eating • from respiration occurs in cells which the water formed is called metabolic water

Ways of Losing Water in Animals • evaporation from body surfaces • sweating • exhalation • urination • defaecation

Hypotonic, Hypertonic and Isotonic Solutions • Hypotonic solution - a solution has a higher water potential than the reference solution

Hypertonic solution - solution has a lower water potential than the reference solution • Isotonic solution - a solution has the same water potential as the reference solution

cells burst in hypotonic solution Animal Cells Response to Different Solutions water move in by osmosis tissue cells

in hypertonic solution cells shrink Animal Cells Response to Different Solutions tissue cells water move out by osmosis

Importance of Osmoregulation • osmoregulation is the maintenance of correct levels of water in the body • any excessive gain or loss of water will upset the proper functioning of cells in an organism • metabolic reactions are affected and organisms may die

Investigation 11.1 Investigation of the Effects of Different Salt Concentration on Red Blood Cells

red blood cell swells and is about to burst red blood cell shrinks red blood cell remains unchanged in appearance In hypotonic saline solution In hypertonic saline solution In isotonic saline solution Which of the five saline solutions most closely resembles the blood plasma in salt concentration ? Ans: The one in 0.8% saline solution is the most resembles the blood plasma concentration.

red blood cell swells and is about to burst red blood cell shrinks red blood cell remains unchanged in appearance In hypotonic saline solution In hypertonic saline solution In isotonic saline solution What evidence supports your answer ? Ans: Red blood cells in 0.8% saline solution remain unchanged in appearance indicating that the solution is isotonic to blood plasma …

red blood cell swells and is about to burst red blood cell shrinks red blood cell remains unchanged in appearance In hypotonic saline solution In hypertonic saline solution In isotonic saline solution What evidence supports your answer ? Ans: Fewer red blood cells can be observed in 0.6% saline solution and even fewer in 0.2% saline solution. This shows the two solution are hypotonic to the red blood cells …

red blood cell swells and is about to burst red blood cell shrinks red blood cell remains unchanged in appearance In hypotonic saline solution In hypertonic saline solution In isotonic saline solution What evidence supports your answer ? Ans: The 1.6% and 3.2% saline solutions are hypertonic to the red blood cells as a net movement of water out of the red blood cells into the saline solution is noticed.

kidney ureter urinary bladder urethra Human Urinary System

Inferior vena cava aorta left kidney renal vein renal artery right kidney ureter urinary bladder sphincter muscle urethra Human Urinary System

Human Urinary System - Location of Kidneys • mammals have two kidneys which are reddish and bean-shaped • they are situated at one on each side of the vertebral column, below the ribs and are not protected by any part of the skeletal system • renal artery brings blood to kidney while renal vein takes blood away from it

Human Urinary System - Ureter • carries urine from kidney down to urinary bladder where stores urine temporarily • valves are present in ureter to prevent urine from flowing upwards • back flow of urine may happen when urinary bladder empties if valves do not close properly.This may lead to infection and damage kidney

Human Urinary System - Urinary Bladder • a muscular bag situated towards the bottom of the abdominal cavity • urethra is led out from it • on the top of urethra is surrounded by ring of sphincter

sphincter muscle relaxes + wall of urinary bladder contracts urination occurs Urination • normally, the sphincter muscle is tightly contracted, so no urination occurs Adults can control the sphincter muscle but children cannot, it relaxes automatically when the bladder is full when urinary bladder is full

cortex medulla nephron renal artery renal vein ureter pelvis Structure of Mammalian Kidney

Structure of Mammalian Kidney • made up of three parts:-a light outer region - cortex - a dark inner region - medulla - a whitish central region leads to kidney - pelvis • contain numerous tiny tubules called nephrons

after leaving the capsule, it coils up (proximal convoluted capsule) Structure of Nephron • consists of a swollen end called Bowman’s capsulewhich is connected to a narrow tubule the tubule begins in cortex

It is then descends into the medulla and becomes U-shaped (loop of Henle) It goes back into the cortex and coils up again (distal convoluted tubule) Finally, it drains into a collecting duct which goes through the medulla and down to pelvis

glomerulus efferent arteriole afferent arteriole distal convoluted tubule (second convolution) renal artery renal vein collecting duct proximal convoluted tubule (first convolution) capillaries around nephron Loop of Henle Nephron

enters Bowman’s capsule afferent arteriole (branches from renal artery) efferent arteriole (capillaries join up) …... How Nephron is Connected with Blood Vessel renal artery Glomerulus (a tightly bunched group of capillaries)

leaves Bowman’s capsule venule (capillaries join up) renal vein How Nephron is Connected with Blood Vessel capillaries (spread out and wrap around tubule)

first & second convolution Bowman’s capsule (with glomerulus) afferent arteriole efferent arteriole loop of Henle collecting duct venule Structure of Nephron

How Nephron Works ? By two ways, one is ultrafiltration and the other is reabsorption

Ultrafiltration • diameter of tiny artery leading to the glomerulus is larger than the leaving one so increase in pressure is resulted as blood tries to force its way out of the smaller tube • the high hydrostatic pressure forces small molecules through the walls of capillaries and Bowman’s capsule into the capsular space

fluid which filtered into the nephron is glomerular filtrate • glomerular filtrate has the same composition as that of blood except that it hasn’t got red blood cells, blood proteins & blood platelets

Reabsorption • reabsorption is the process of absorbing useful substances into capillaries which wrapped around tubule • as in glomerular filtrate, some substances like glucose and amino acid are useful to human so they are absorbed back while fluid travels along the tubule

those urea which remains in the fluid pass the whole nephron and finally drains into collecting duct which leads to pelvis and form urine • urine contains mostly water, with urea and excess mineral salts

reabsorption of glucose, amino acids and some salts begins in the first convolution and finished when the fluid reaches loop of Henle

useful substances are reabsorbed by diffusion down the concentration gradient and active transport against concentration gradient • in collecting duct, water is mainly reabsorbed by osmosis but the first convolution actually reabsorbs the largest amount of water

Functions of Kidney • kidney mainly has three functions: • osmoregulation • removal of excess salt • excretion

blood becomes diluted small proportion of water is reabsorbed dilute urine produce Functions of Kidney - Osmoregulation drink a lot of water Amount of water in blood: CONSTANT

blood becomes concenrtrated large proportion of water is reabsorbed concentrate urine produce Functions of Kidney - Osmoregulation after sweating Amount of water in blood: CONSTANT

concentration of urine is higher salt enters blood, concentration of salt in blood increase volume of urine increase man feels thirsty drink water Functions of Kidney - Removal of Excess Salt after eating a salty meal

Functions of Kidney - Excretion • protein cannot be stored in human body, excess protein are broken down in liver • removing of amino groups from amino acids is called deamination • amino groups are incorporated into urea molecules and then excreted in urine

Kidney Failure and Artificial Kidney • some kidney diseases can lead to kidney failure which kidney can no longer function properly • toxic substances will accumulate in blood and patient will die

artificial kidney is a bulky machine attached to patient which is used to filter and clean patient’s blood • artificial kidney make use of the principle of dialysis. It has a filter made of cellophane which acts as a selectively permeable membrane

along one side of the membrane is the patient’s blood while the other side is dialysis fluid which has the same contain as plasma except urea • only urea diffuses from patient’s blood into dialysis fluid through cellophane filter • blood without urea will return to patient through his vein

dialysis fluid flows in direction opposite to that of blood flow to increase the efficiency of diffusion of urea into dialysis fluid • other than using artificial kidney, kidney transplant is another possible method but only few people are willing to donate their kidneys after death

Excretion in Human • metabolism are reactions take place inside cells of an organism • most of the by-products of metabolism are toxic and should be removed once they are produced by excretion • there are four major excretory organs in human body: Lungs,Kidneys,Liver and Skin

Excretory Organs - Lungs • excrete carbon dioxide which is produced by cells during respiration and is carried by blood to lungs • carbon dioxide diffuses out of the blood capillaries surrounding the lungs and passes into the air sac • it is excreted when people breathe out. Water is lost during respiration, too

Excretory Organs - Kidneys • deamination (break down of excess amino acids) in liver forms urea and uric acid • urea and uric acid are called nitrogenous wastes • the wastes are carried by blood to kidneys which excrete them from the body in form of urine

Importance of Water