Biology F211

Animal cells:

• plasma membrane
• lysosome
• ribosome
• rough endoplasmic reticulum
• nuclear envelope
• nucleolus
• nucleus
• golgi apparatus
• smooth endoplasmic reticulum
• mitochondra

Plant cells:

• all as above
• cell wall with plasmodesmata
• vacuole
• chloroplasts

Protein production:

• instructions are in the DNA in the nucleus
• the nucleus copies the instructions from DNA to mRNA
• the mRNA leaves the nucleus through the nuclear pore and attaches to a ribosome on the RER
• the ribosome reads the instructions and uses codes to assemble the protein (amino acids)
• the protein is pinched off in a vesicle and transported to the golgi apparatus which recieves, modifies and packages the protein before sending it in a vesicle to the cell membrane (to be secreted).

Cytoskeleton (microtubules/microfillaments) - four functions:

• support organelles, keeping them in position
• help strengthen and maintain the shape of the cell
• transport materials e.g. chromosomes
• allow cell to move e.g. cilia and undulipodia

Prokaryotes:

• extremely small (less than 2um)
• circular DNA
• no nucleus
• cell wall made of polysaccharide
• few organelles
• small ribosomes
• e.g. bacterium E. Coli

Eukaryotes:

• larger cells (2-200um)
• linear DNA
• nucleus
• no cell wall (animals), cellulose (plants), chitin (fungi)
• lots of organelles
• larger ribosomes
• e.g. human liver cell

Magnification = Image/object, Resolution is detail (distinguish between 2 points)

Light microscope:

• 0.2um resolution
• x1500 magnification
• 2D
• staining - use dye (contrast) e.g. methylene blue

TEM

• 0.001um resolution
• x500,000 magnification
• 2D                                          

SEM

• 0.005um resolution
• x100,000 magnification
• 3D

Plasma:

• cells can enter and leave
• partially permeable
• recognition by other cells e.g. immune system
• allow cell communication
• phospholipid bilayer - 7mm thick

within cells:

• around organelles - divide into compartments - functions more efficiently
• sometimes folded increasing surface area and more efficient reactions e.g. cristae of mitochondria
• can form vesicles for transport
• control which substances enter and leave organelles e.g. RNA
• partially permeab;e

Protein channels:

• allow small charged particles through
• form pores in membrane
• different proteins for different particles

Carrier proteins:

• large molecules
• protein changes shape
• molecules binds to receptor
• different proteins for different molecules

Carrier proteins (active transport):

• molecules and ions
• molecule binds to receptor and protein changes shape
• ATP is used
• e.g. calcium ions

Glycolipids and Glycoproteins:

• stabilise membrane by forming hydrogen bonds with water
• sites where drugs, hormones and antibodies bind
• receptors for cell signalling
• antigens - immune response
• glycolipid - phospholipid with carbohydrate chain attached
• glycoprotein - protein with carbohydrate chain attached

cell signalling:

• cells communicate using messenger molecules
• one cell releases messenger
• travels to target cell
• binds to receptor on cell membrane
• receptor proteins have specific shape - only messengers with a complementary shape can bind to them
• e.g. glucagon (hormone)

Drugs:

• drugs work by binding to receptors
• either to trigger a response or block a receptor and prevent it from working
• e.g. histamine causes inflammation, antihistamine blocks histamine receptors

Temperature and permeability:

• below 0oC - rigid, proteins denature increasing permeability, ice crystals may form (pierces membrane)
• between 0oC and 45oC - can move, partially permeable, as temp increases so does kinetic energy so increases permeability.
• above 45oC  - bilayer melts, meaning more permeable, the water in the cell expands putting pressure on the membrane, proteins denature increasing permeability

Diffusion rate depends on:

• concentration gradient - higher = faster rate
• thickness of exchange surface
• surface area - larger = faster rate

Osmosis:

• high - low water potential
• pure water has highest water potential

Cells - in pure water:

• animal - haemolysed - (burst)
• plant - turgid - (membrane pushes against cell wall)

Cells - in sugar solution:

• animal - crenated - (shrinks)
• plant - plasmolysed - (membrane pulls away from cell wall)

Endocytosis:

• too large e.g. proteins, lipids
• cell can surround with section of plasma membrane
• pinches off to form vesicle inside the cell (ingested substances)
• e.g. phagocytes

Exocytosis:

• released from glogi apparatus
• vesicles move toward membrane
• fuse and release contents outside (excrete)
• some inserted straight into the plasma membrane (proteins)

Importance of mitosis:

• asexual reproduction
• growth
• repair
• replacement, e.g. skin cells

Cell cycle:

Interphase - replication of DNA and organelles

Mitosis

Cytokinesis - cytoplasm divides

Growth

PROMAT

Prophase:

• chromosomes visible
• shorten and thicken (supercoil)
• consist of sister chromatids
• nuclear envelope breaks down and disappears
• centriole divides and move to opposite ends forming spindle (protein fibres)

Metaphase:

• chromosomes line up at equator
• each becomes attached to a spindle thread by centromere

Anaphase:

• replicated chromosomes seperate
• sister chromatids seperate when centromere splits
• 'sisters' become individual chromosomes
• spindle fibres shorten pulling toward poles

Telophase:

• two new nuclei form
• as the new chromosomes reach poles a new nuclear envelope forms each set
• spindle breaks down and disappears - can no longer see uncoiled chromosomes under a light microscope 

Cytokinesis:

• cell splits into two new cells, each containing a full set of chromosomes
• the product is genetically identical to sister and parent cell.

Cell cycle - plants and animals:

• animals - most cells are capable
• plants - only meristem cells can divide this way

Budding - yeast cells:

• asexual production - mitosis
• Bud forms at surface
• cell undergoes interphase - DNA and organelles replicate
• cell undergoes mitosis
• nuclear division completes
• bud seperates off
• genetically identical yeast cells

• genetically different cells
• chromosomes swap bits during meiosis and each gamete gets a combination of half of them at random
• there are two divisions - chromosome number is halved, then chromosomes split in half.
• homologous pairs - chromosomes are same size and have same genes but different versions (alleles)
• four haploid daughter cells that are genetically different to each other and the parent cell.

stem cells - unspecialised, they differentiate to become specialised

Bone marrow:

• in bone marrow adult stem cells divide and differentiate to replace worn out blood cells,
• differentiate into erythrocytes (red) and neutrophils (white)

Cambium:

• stem cells divide and differentiate to become xylem and phloem
• cells divide and grow out from the ring (that vascular cambium forms), differentiating as they move away from the cambium

Neutrophils (white):

• flexible shape allows to engulf pathogens - many lysosomes to break down engulfed particles

Erythrocytes (red):

• biconcave shape provides large surface area for gas exchange, no nucleus gives more room for haemoglobin

Epithelial cells:

• interlinking cell membranes and have cilia or microvilli - folds in membrane that increases surface area.

Sperm cells:

• flagellum (tail), lots of mitochondria for energy and acrosome containing digestive enzymes

Palisade mesophyll cells:

• contain chloroplasts for absobtion of sunlight (photosynthesis) - thin walls so C02 cand easily diffuse in.

Root hair cells:

• large surface area and thin permeable wall for entry of water and ions, cytoplasm contain mitochondria for ATP for active transport

Guard cells:

• line stomata - used for gas exchange, in light they take up water and turgid.
• thin outer walls, thickened inner walls force to bend outwards - opening stomata for photosynthesis

1. Squamous epithelium:

• single layer of flat cells, many places including alveoli.

2. Xylem:

• transports water and supports plant, contain xylem vessel cells (pits) and parenchyma cells

3. ciliated epithelium:

• covered in cilia

4. Phloem:

• transports sugars, arranged in tubes, made up of sieve cells, companion cells.
• each sieve cell has holes (sieve plates) so sap can move easily through them

Tissues - collection of cells that are similar to each other and perform a common function.

Organs - a collection of tissues working together to perform a particular function, e.g. leaves of plants, liver of animals.

Organ system - number of organs working together to perform an overall life function, e.g. reproductive system

Multicellular organisms have developed different systems of cooperation between different cells:

• Transport systems, e.g. humans, the circulatory system
• Communicative systems - both animals and plants have chemical communication systems that use messenger molecules. Animals also have a nervous system

Exchange surface - a specialised area that is adopted to make it easier for molecules to cross from one side to another

why?:

• cells need to take in oxygen (for aerobic respiration) and nutrients
• need to excrete waste products like carbon dioxide and urea

Smaller animals have higher surface area to volume ratio

Exchange organs:

• in single celled organisms important substances can diffuse quickly in and out of the cell across the cell surface membrane - quick diffusion rate.
• In multicellular organisms diffusion is too slow:
• - some cells are too deep within the body, big distance to outside environment
• -  have low surface area to volume ratios which means its difficult to exchange enough substances to supply all cells - Exchange Organs 

Examples (other than lungs):

• small intestine, nutrients are absorbed
• liver, sugar levels
• root hairs of plants - water is absorbed
• hyphae of fungi

Most gas exchange surfaces have adaptations:

• have a large surface area - increases rate of diffusion
• thin walls - short diffusion pathway - increases rate of diffusion
• maintains steep concentration gradient - increases rate of diffusion

Lungs adapted:

• Many alveoli - large surface area
• Barrier - permeable to oxygen and carbon dioxide
• Alveolar epithelium and capillary endothelium - 1 cell thick - short distance
• Alveoli have good blood supply - capillaries take away oxygen and bring carbon dioxide maintaining the concentration gradient
• ventilation of lungs refreshes air in alveoli and keeps concentration gradient high.

Gaseous Exchange system:

• Goblet cells - secret mucus that traps microorganisms
• Cilia - beats mucus away from alveoli to back of throat
• Elastic fibres - breathe in they strech, breath out recoil - help push air out
• Smooth muscle - allow control of diameter, can relax (less resistance to air)
• Rings of cartilage - provide mechanical support - prevent collapse of trachea

Inspiration:

• Intercostal muscles and diaphragm contract (flattens)
• ribs raise
• volume of chest cavity increases (thorax)
• pressure drops to below atmospheric pressure
• air moves into lungs
• requires energy - active

Expiration:

• intercostal muscles and diaphragm relax (cuves)
• ribcage move down and in
• volume of thorax decreases
• pressure increases to above atmospheric pressure
• air moves out of lungs
• doesn't require energy - passive

Tidal volume:

• volume of air moved in and out of lungs with each breath when you are at rest
• normally around 0.5 dm3

Vital capacity:

• maximum volume of air that can be breathed in or out
• varied but normally 5dm3

Breathing rate:

• breaths per minute

Oxygen uptake:

• volume reduction x 60/ time of all breaths

Multicellular organisms:

• harder to supply cells as relatively big and has low surface area to volume ratio
• very active - respiring quickly
• need constant rapid supply of glucose and oxygen - needs transport system
• mammals - circulatory system uses blood

Single circulatory system:

• blood only passes through the heart once for each complete circuit of body
• e.g. fish
• heart -> gills -> rest of body

Double circulatory system:

• blood passes through heart twice for each complete circuit of body
• e.g. mammals
• right side -> lungs -> left side -> body (blood to lungs is pulmonary system, blood to body is the systemic system)

Vertebrates:

• closed (blood is inclosed inside blood vessels)
• blood -> arteries -> capillaries -> veins -> heart

Invertebrates:

• open (blood not enclosed)
• flows freely in the body cavity
• heart (segmented) -> contracts -> main artery -> body cavity -> values

1. Diastole:

• atria and ventricles relax
• blood flows into atria through the AV valve and into the ventricles

2. Atrial systole:

• atria contract
• pushes blood into ventricles
• pressure in ventricles causes AV valve to snap shut (prevent backflow)

3. Ventricular systole:

• all four valves closed
• then ventricles contract raising pressure in the ventricles
• semilunar valves open
• blood pushed out of heart

• Sino atrial node (SAN) initiates a wave of excitation that spreads over the walls of the atria - atrial systole
• the wave cannot get past the non conducting collagen tissue between the atria and the ventricles
• at the top of the septum is the AV node - the excitation is delayed to allow atria to empty
• after delay - spreads to Bundle of His, and then onto the purkyne tissue in the ventricle walls
• causes contraction of ventricle walls, ventricular systole, from the apex upwards.

ECG

P - contraction of atria

QRS - contraction of ventricles

T - diastole

Arteries:

• small lumen
• collagen wall
• elastic tissue
• smooth muscle
• endothelium folded

Vein:

• large lumen
• collagen
• smooth muscle
• elastic tissue
• valves

Capillary:

• very thin walls
• narrow lumen

Tissue fluid - role is to transport oxygen and nutrients from the blood to cells, and to carry carbon dioxide and wastes from the cells to the blood. (It bathes cells)

How it is formed:

• at the arterial end of a capillary, blood is under high pressure (hydrostatic)
• this causes fluid to be pushed out of capillaries through tiny gaps
• fluid that leaves consists of plasma with dissolved nutrients and oxygen
• this is tissue fluid
• water tends to move back into the blood from tissue fluid by osmosis, down a water potential gradient
• at the vein end of the capillary blood has lost the hydrostatic pressure allowing tissue fluid to move back into the capillary

Formation of lymph:

• some tissue fluid is drained into the lymphatic system - consists of vessels
• lymph fluid is similar to tissue fluid (sam solutes) but lymph contains more CO2 and wastes absorbed by body cells and more fatty material
• lymph contains lymphocytes - produced by lymph nodes which filter any bacteria and foreign material - lymphocytes can engulf and destroy this material as part of the immune system

Blood:

• cells - erythrocytes, leucocytes, platelets
• proteins - hormones, plasma proteins
• fats - lipoproteins

Tissue fluid:

• cells - some phagocytic white blood cells
• proteins - hormones, and proteins secreted by body cells
• fats - none

Lymph:

• cells - lymphocytes
• proteins - only antibodies
• fats - more than in blood

• oxygen is transported in erythrocytes (red blood cells) which contain haemoglobin.
• Haemoglobin + oxygen = oxyhaemoglobin
• iron haem group has an affinity for oxygen - each haemoglobin can carry four oxygen molecules
• oxyhaemoglobin is able to release oxygen -dissasociation
• fetal haemoglobin has a higher affinity than adult haemoglobin

Bohr effect:

• when CO2 is present, haemoglobin is less saturated with oxygen
• because hydrogen ions displace oxygen
• CO2 -> (carbonic anhydrase) -> carbonic acid
• carbonic acid -> hydrogen ions and hydrogencarbonate ions
• haemoglobin takes up hydrogen ions and forms haemoglobinic acid
• hydrogencarbonate ions are transported in blood plasma
• when blood reaches lungs the low pCO2 causes hydrogen ions and hydrogencarbonate ions to recombine as CO2

Xylem:

• transport of water and mineral ions
• xylem vessels, long tube like joined end to end (uninterupted tube)
• the cells are dead - no cytoplasm
• walls - thickened with lignin (for support), they prevent collapse
• water and ions move into the vessels through small pits in the wall where there is no lignin.

Phloem:

• transport of sucrose, consist of phloem fibres, and parenchyma cells
• sieve tube elements - living cells, sieve plates form holes in end walls, have no nucleus and few organelles, cytoplasm is connected through the sieve plates.
• companion cells - lack of nucleus in sieve tubes means can't survive without help, there is a companion cell for every sieve tube, carry out living functions for themselves and sieve tube, provide the energy for ATP active transport of solutes

Water uptake from soil:

• root hair cells absorb minerals by active transport using ATP, minerals reduce the water potential
• so the water potential in the cell is lower than the soil
• osmosis occurs

Through the root to the xylem:

• apoplast pathway - water filled spaces between cell walls, does not pass through the plasma membranes.
• symplast pathway - through the cytoplasm and the gaps in cell walls (plasmodesmata)
• vacuolar pathway - similar to symplast but through vacuoles as well.
• through root cortex, within root cortex is the endodermis cell layer which contains casparian ***** (waxy) which blocks the apoplast pathway.

How does water move up?

• Root pressure - action of endodermis moving minerals into xylem by active transport drives water into xylem by osmosis
• Transpiration pull - loss of water by evaporation causes tension, cohesive tendencies of water causes the transpiration stream. This is the cohesion-tension theory
• Capillary action - attraction of water to the sides of the xylem vessel is adhesion which causes water to be pulled up the sides of the vessel.

At the leaves:

• water leaves xylem by apoplast pathway
• evaporates from cell walls into spaces
• when stomata open, water moves out down the water potential gradient into air.

Transpiration

• loss of water by evaporation from the aerial parts of a plants
• osmosis from xylem to mesophyll cells
• evaporation from surface of mesophyll cells into intercellular spaces
• diffusion of water vapour from intercellular spaces out through stomata

Factors affecting transpiration rate:

• leaves - surface area
• stomata - number, size, position
• cuticle - reduces evaporation (waxy)
• light - stomata open, increases rate
• temp - as increases, it increases evaporation inside leaf as molecules have more kinetic energy, this creates a greater water potential gradient.
• humidity - higher will decrease
• air movement - higher will increase
• water availability

Transpiration is unavoidable:

• plants exchange gases with atmosphere via stomata
• during day plants take up CO2 used in photosynthesis
• also must remove oxygen so stomata must be open

Xerophytes - adapted to reduce water loss:

• smaller leaves - small surface area
• thick waxy cuticle - reduces evaporation
• closing stomata when water availability is low
• hairs on surface - trap moisture
• pits containing stomata
• rolling leaves - trap air
• e.g. marram grass

Translocation:

• transport of assimilates throughout plant
• source - releases sucrose into phloem e.g. leaves
• sink - removes sucrose from phloem e.g. storage organs, meristems in roots
• active process

How does sucrose enter the phloem?

• ATP is used by companion cells to transport hydrogen ions out and into the surrounding tissue.
• this creates a diffusion gradient and hydrogen ions diffuse back with sucrose with the help of cotransporter proteins
• as concentration of sucrose in companion cells increases - they diffuse into sieve tube elements through plasmodesmata.

Mass flow:

• sucrose is activeley loaded into the sieve tube element which reduces the water potential
• water therefore flows into the sieve tube element by osmosis which increases the hydrostatic pressure
• the water moves to lower hydrostatic pressure
• sucrose is then removed by surrounding cells, which increases the water potential inside the sieve tube element
• water moves out of the sieve tube by osmosis and reduces the hydrostatic pressure

Evidence for mass flow:

• aphid mouthparts take food from phloem
• ringing tree results in sugars collecting - evidence of downward flow
• companion cells have many mitochondria
• concentration of sucrose is higher in the source than the sink