research: cellular homeostasis

Root hair cells

The root hair cells in plant roots use active transport to absorb mineral ions such as nitrates from the soil- even though there are lower concentrations of minerals in the soil than there are within the root hair cell.

source: https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi81JS04WHbWlNcswE4KGiSAb3bgekuAkcU7fzkP4w_eGjPgQkCWESDUu1gB6aoZdegvvDjc7vel_rPIfCpPPAI-af-XBXcsEqvoSWHXZL704u1xwGNAjWfoV_g0BKpocQz2MhLGFhL4vtY/s400/gb110711_root_hair_apoplast_and_symplast.jpg

Root hair cells have a large surface area to speed up the process of osmosis. The cell sap in the vacuole is hypertonic (low concentration of water molecules), hence causing water to pass through the partially permeable cell membrane by osmosis. This results in a high concentration of water molecules and a lower concentration of cell sap containing sugars, organic acids and ions. The water will then osmosize into the next cell, travelling from a region of high concentration to a region of low concentration. 


Small intestine villi cells

The small intestine villi cells use active transport alongside diffusion to maximise the absorption of glucose and other substances (eg minerals).

source: http://www.acbrown.com/neuro/Lectures/Mmbr/AVFigs/NrMmbr51.jpg 

The villus is made up of many cells to increase the surface area and therefore the rate of diffusion. The microvillar membrane of the microvilli (found on surface of every cell in villus) is packed with enzymes to maximize the breakdown of complex nutrients into simple compounds. 

video viewing: BBC worldwide fish and frogs living out of water

In your online journal, consider these questions as you view the video and put in your own thoughts after viewing this video. 

1) What are the differences or similarities in the strategies that they have employed?

Both the lung fish and the desert frog entomb themselves in the earth and have unique body bags as protection against droughts. The lung fish coats itself in mucus which dries as a body bag to seal itself off from the drought, while the desert frog  sheds layers of skin that form a water proof barrier which prevents the frog from drying out. 

The thorny devil and the desert frog can both survive long periods of time without water. The thorny devil lives off of black ants that provide moisture it needs and collects water by capillary action, while the desert frog has a reservoir of drinkable water in its bladder. 

2) From what you understand about Homeostasis so far, how do you think these strategies allow for homeostasis to occur?

By sealing itself off from the heat of the drought, the lung fish and the desert frog are able to maintain homeostasis as it prevents the external environment from being too extreme and different from its internal environment. This strategy also allows them to maintain moisturised during this dry period. 

By using capillary action, the thorny devil is able to consume enough water to stay moisturised and hydrated. This strategy also allows the thorny devil to maintain its body temperature by keeping cool. Eating black ants also allows the thorny devil to consume enough water to maintain homeostasis between a more hydrated and cooler internal environment as compared to the dry and hot external environment of the desert. 

cell membrane (tbc)

Function of cell membranes

1. To compartmentalize the cell as seen in the different organelles.

• different metabolic processes require different enzymes & conditions
• compartmentalization provides optimum conditions for the reaction to occur without interference from other enzymes and factors
• it also prevents autolysis of cells, e.g. enzymes of pancreatic juice are found in vesicles prior to their secretion

2. Increases surface are for exchange of substances

• e.g. microvilli of intestinal cells making up the villi 

3. Cell recognition

• Membranes contain certain protein/ glycoprotien/ glycoplipids molecules which act as identity markers. (e.g. antigens on red blood cells) 

4. Cell communication

• Some proteins/ glycolipids/ glycoproteins embedded in the membrane act as receptors for hormones and neurotransmitters. 
• Communication pathway: cell receptor + hormone --> cell to take up glucose

5. Site of chemical reactions

• e.g. light reactions of photosynthesis take place on thylakoid membranes found in chloroplasts

6. Controls entry and exit of substances

• e.g. separates cytoplasm from external environment, maintaining constant environment inside the cell. (Cellular Homeostasis / Homo Stasic) 

Types of Transport

There are ways that substances move through the membrane:

1. Passive transport

• does not require ATP
• driven by concentration gradient (concentration difference) - moving down its concentration
• occurs in both living and non- living systems
• simple diffusion/ diffusion (oxygen. CO2. minerals in soil, etc)
• osmosis (water only) 
• facilitated diffusion- carrier proteins and pores which increases diffusion rate

* Diffusion: 

Diffusion is the spread of particles through random motion from regions of higher concentration to regions of lower concentration 

* Osmosis:

Osmosis is the net movement of water molecules across selectively permeable membrane from an area of less negative (high) water potential to an area of more negative (lower) water potential. 

2. Active transport

• requires the use of energy (ATP)
• against the concentration gradient
• occurs only in living systems

Diffusion

The type of substances that undergo simple diffusion are: 

• small, non-polar, hydrophobic
• lipid soluble/ non-polar
• small polar (slower), hydrophilic

Simple diffusion:

- Hydrophilic molecules diffuse into cells very slowly, because of repulsion faced in the hydrophobic interior core of the lipid bilayer

- Oxygen, carbon dioxide, fatty acids and steroids are hydrophobic molecules, diffuse rapidly through the membranes. 

Facilitated diffusion:

- Type 1: Transmembrane proteins create a water-filled pore through which ions and small hydrophilic molecules can pass by diffusion. Channel protein can open and close like a gate.

-Type 2: Some molecules are too large for ion channel (e.g. amino acids, glucose) // Solution = carriers // Carrier protein has specific binding site; once substance binds --> conformation change of protein occurs; helps to move larger substances across. releases and then returns back to original conformation 

1. Substances are transported against their concentration gradient by specific proteins.
2. Transport is specific carrier can only recognise specific molecules/ ions
3. ATP is required to provide energy
4. Example: proton pump 

Active Transport

1. Endocytosis (Bulk Transport)

There are two types of endocytosis: 

1. Phagocytosis (takes in solid)

• Formation of pseudopodia

2. Pinocytosis (takes in liquid) 

• Invagination of cell membrane

2. Exocytosis (Bulk Transport)

Where secretory vesicles fuses with cell surface membrane

Examples:

• Secretion of extracellular enzymes, hormones and antibodies
• Removal of waste products of digestion 

I

essay: glucose regulation during obs

During OBS, physical activities such as kayaking and trekking are carried out. During these activities, tissues cells from all over the body rapidly use up glucose in our blood stream, to be used in aerobic respiration. Aerobic respiration occurs in the mitochondria of our cells, which involves a cascade of reactions, eventually breaking down glucose into energy, which our bodies require to perform the strenuous physical activities at OBS.

When glucose levels in our blood fall, homeostasis occurs. The cells in the pancreas’s Islets of Langerhans monitor the levels of glucose in the blood. The pancreas receptors in our blood vessels detect the drop in blood glucose levels, hence releasing less insulin and more glucagon to target the liver. Glucagon is a hormone whose effects on liver cells act to increase the blood glucose levels. Glycogenolysis (the conversion of glycogen into glucose) then takes place and glucose is released back into the blood stream, increasing blood sugar levels. The glucose will then be broken down into energy. This gives us the energy we require for the activities during OBS. However, when the levels of blood sugar rise, a different hormone from the beta cells in the Islets of Langerhans can also be found. This hormone is insulin. Insulin causes Glycogenesis (conversion of glucose into glycogen), which is the reverse process of Glycogenolysis, hence decreasing blood sugar. This negative feedback controls the amount of blood glucose levels, ensuring that there is regulation in the blood sugar levels.

cell structures

lesson structure: 

cell structure --> functions --> cell surface membrane --> transport across membrane

a recap: 

parts	functions
a: nucleus	contains the genetic material (DNA) controls all the cellular activities
b: cytoplasm	consists of cytosol and organelles cytosol (cyto: cell ; sol: gel) is a aqueous matrix where organelles are suspended
c: vacuole	fills with food being digested and waste material that is on its way out of the cell.
d: cell membrane (cell surface membrane; plasma membrane)	it controls the movement of substances in and out of the cell
e: mitochondrion	produces energy in the form of ATP (adenosine triphophate) for the cell and body
f: golgi apparatus	packages proteins and carbohydrates into membrane bound vesicles to be synthesised by the cell
g: lysosomes	contains digestive enzymes digestion of cell nutrients take place.
h: smooth endoplasmic reticulum (er)*	transports materials through the cell contains enzymes and produces and digests lipids (fats) and membrane proteins buds off from rough ER, moving the newly-made proteins and lipids to the golgi body, lysosomes, and membranes
i:  rough endoplasmic reticulum (er)*	has ribosomes transports materials through the cell and produces proteins in sacks called cisternae (which are sent to the golgi body, or inserted into the cell membrane).
j:  ribosomes	composed of RNA- rich cytoplasmic granules protein synthesis takes place here

chloroplast

converts H2O and CO2 using light energy from the sun into soluble sugars for the plant

*endoplasmic reticulum

endo: internal
plasmic: within the cell
reticulum: net-like structure

rough er: has ribosomes
smooth er: no ribosomes

*vesicles are used to ensure transportation within the cell, and ensures that it will not diffuse out into the cell